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Dark Adaptation of the Human Eye and the Value of Red Flashlights (U.S. National Park Service)

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Dark Adaptation of the Human Eye and the Value of Red Flashlights (U.S. National Park Service)

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Dark Adaptation of the Human Eye and the Value of Red Flashlights (U.S. National Park Service)

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By Jim O’Connor of the Tucson Amateur Astronomy Association

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Bright city lights are bringing spring forward and pushing autumn back

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Bright city lights are bringing spring forward and pushing autumn back

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Light pollution affects plants as if it were the Sun, accelerating the sprouting of leaves and postponing their fall

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Light pollution affects plants as if it were the Sun, accelerating the sprouting of leaves and postponing their fall

Barcelona, where the growing season for plants has been extended by 14 days. Artur Debat (Getty Images)

Streetlights, neon lights, and LEDs in shop windows are confusing plants: in cities, spring arrives several days earlier than in the countryside, and autumn is also delayed by almost two weeks. Research published in the scientific journal Nature Cities shows how light pollution acts like the Sun, accelerating fundamental processes in plant phenology, such as budding and leaf fall. Researchers believe that city lights are altering plant life, the consequences of which are yet to be determined.

Light pollution already prevents us from seeing the stars. Recent studies have also shown how excessive artificial lighting in cities may be affecting the behavior of urban animals and human health. At the same time, many studies have confirmed that spring arrives earlier in cities. But they pointed to global warming, which is intensified in urban environments by the so-called urban heat island effect: the concrete of buildings, the asphalt on the streets, the height of buildings, and the entire urban design trap heat. Now, light pollution is added to the equation, and the result is the widespread disruption of urban vegetation.

Although U.S. cities are brightest in spring, European cities outshine American cities in autumn, which arrives later in Europe. NASA.gov

The study found that, on average, city centers turn green about 12.6 days before plants in the surrounding countryside. At the other extreme, leaf senescence begins in cities an average of 11.2 days earlier. The phenomenon is also widespread. The study tracked the start of the plant growing season in 428 large cities in the northern hemisphere. In 378 of them, or 88.3%, they observed these changes in plant phenology. To detect these changes, they used sensors from several satellites and data collected since 2014.

"Satellites detect differences in greenness by measuring the amount of light reflected from the Earth's surface," explains Lin Meng, a researcher at Vanderbilt University (United States) and a co-author of the study. They carry instruments on board that capture this reflection at different wavelengths, particularly in the visible and near-infrared (NIR) parts of the spectrum. "Vegetation strongly reflects NIR light while absorbing visible red light for photosynthesis," Meng adds. They capture this using markers such as the Normalized Difference Vegetation Index (NDVI). "Areas with denser vegetation or higher photosynthetic activity reflect more NIR light and less red light, resulting in higher NDVI values," the researcher explains.

By comparing these reflectance patterns in cities and nearby countryside, satellites were able to detect spatial changes in greenness. The study uses a gradient from the most remote areas to the city center itself. In the case of Barcelona, for example, the rural area monitored for comparison is located 32 kilometers (19.8 miles) from the city center. In the Catalan capital, they found that the growing season is 14 days longer in the urban core compared to the more remote rural areas.

Panoramic view of Bilbao at night, highlighting the discreet lighting of the Guggenheim Museum and the light emanating from the Iberdrola Tower. Fernando Domingo-Aldama

The other major contribution of this work is that it manages to disaggregate the causes of this urban-rural differential. The authors also used satellites to measure the degree of light pollution. Under natural conditions, on a cloudy night, luminosity is around 0.6 millilux (a lux measures the amount of incident light). If there are no clouds, with a full moon at its zenith, the figure can reach 0.3 lux. But in cities, the luminosity ranges from 7 to 65 lux. Previous studies have shown how the nighttime environment has become almost 10% brighter each year for more than a decade. But until now, temperature has always been cited as an explanation for phenological changes in urban flora.

"We used a statistical analysis method - partial correlation analysis - to disaggregate the impact of temperature from the impact of artificial lighting on vegetation phenology," Meng explains. "Partial correlation measures the degree of association between two random variables, eliminating the influence of a set of control variables. This allows us to isolate the effect of each factor on the target factor while controlling for other factors." The researchers found that both temperature and light variables affect the length of the plant growing season. They also found that the latter has a greater impact in four of the seven major climatic regions covered by the study, ranging from warm, dry cities like Dallas to cold, dry cities like those in Canada.

Meng adds some detail about cities: "Cities with higher artificial light intensity have a greater impact on phenology," she says. Since levels vary seasonally, their influence differs between spring and fall. "In particular, many American cities showed higher luminosity during spring. In contrast, European cities have higher light pollution in the fall, so they showed a greater influence at the end of the growing season," she adds.

Regarding the consequences for flora, Dunxian She, a professor at Wuhan University (China) and lead author of the study, points out that an earlier spring and a later autumn can have both positive and negative effects. "In natural ecosystems, a longer growing season could improve productivity and carbon sequestration, thus contributing to climate change mitigation. However, it could also affect local ecosystems if new species become more dominant, leading to changes in biodiversity, especially with the introduction of exotic species for urban landscape design," he says.

Artificial light lengthens the photoperiod, acting as an extension of daylight. For the authors of the research, this lengthening could alter the accumulation of signals that initiate budding or senescence, such as a reduced efficiency of photosynthesis. But the disorder goes deeper. Plants perceive light differently depending on its wavelength. Photochromes are proteins that function as photoreceptors, while cryptochromes function as photoreceptors for blue light. The latter is the driving force behind the LED revolution, and the consequences of this remain to be investigated.

Georg Wohlfahrt is the head of the biometeorology group at the University of Innsbruck (Austria). Although he did not participate in this work, he was the lead author of a pioneering paper that found that spring was arriving earlier in cities. His work pointed to the heat island effect and environmental pollution, but also recognizes the role of light pollution. "Apart from non-seasonal climates, such as the tropics, plant phenology depends on temperature and the quality/quantity of light," he recalls in an email. "Artificial light in urban areas modifies plant light exposure and, therefore, phenology. This is not new. The novelty of the Nature Cities article is that it addresses the problem on a large scale in a large number of cities and attempts to disentangle the effect of artificial light from that of the urban heat island," he adds.

If anyone knows about light pollution, it's Christopher Kyba. A professor at the GFZ Helmholtz Research Centre for Geosciences in Germany, he has been researching the impact of artificial light for over a decade. To this end, he's created a network of scientists, citizen science projects, and even an app to measure the loss of nighttime. The results of his latest project have just been published in the same issue of Nature Cities, unrelated to the study of the 428 cities. The citizen science work coordinated by Kyba collected data from 33 German municipalities, finding that, after midnight, more than one light per inhabitant remains on. What's revealing is that for every streetlight left on, there's an illuminated advertisement or shop window.
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"I see reasons for both hope and fear," Kyba says about the future of light pollution. "On the one hand, there are examples of cities and even entire countries in wealthy, industrialized areas of the world where we see decreases in light emissions after midnight," he says in an email. "On the other hand, the vast majority of cities and countries around the world continue to increase their lighting."

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Starlink satellites are censoring the stars

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In some ways, the stars above us are the ultimate equalizer: we're all equally far away, we all share the right to look up at them; and, tiny glittering pinpoints that they are, when we contemplate that cosmic glow, our fractious lives seem so brief, so comfortingly insignificant, compared to the light years they've traveled to meet our eyes. Vast, dark expanses glittering with stars are the skies under which we evolved: every creature alive has countless ancestors who existed under the light of stars visible thanks to the velvety darkness of the night sky.

But industrialization has changed that, of course, by introducing light pollution that gradually erased the stars from view before the bright blue light of countless LEDs made the situation so much worse. And now, as the new space race heats up, spawning tens of thousands of satellites in orbit around the Earth, it only stands to make the visible night sky less so. Dimming stars are just one of many problems posed by satellites and especially megaconstellations, groups of hundreds or thousands of small satellites that work together to give us broadband internet and mobile connectivity.

Starting in the 1950s and up to 2019, there was a sum total of roughly 2,000 operating satellites in orbit. But in May of 2019, Elon Musk's aerospace company SpaceX launched the first megaconstellation, Starlink, with an initial 60 satellites. (The small satellites that make up a megaconstellation launch in groups, with Starlink for example typically sending up 50 small satellites at a time.) But since that fateful launch, several thousand other satellites have made their way into orbit, with many, many more on their way.

"It's like many, many thousands of rotating, glinting ruffled potato chips."

It's still not wall-to-wall satellites in low Earth orbit, but it seeming will be in the near future. (Astrophysicist Dr. Jonathan McDowell keeps a running list here.) The U.S. Federal Communications Commission has already approved well over 7,000 further satellites, and SpaceX alone is aiming to get tens of thousands of their own into LEO over the next decade.

"We have our version of the famous 'hockey stick' plot from climate change, where the temperature is up, steady, steady, steady and [then] rapidly increasing. That's what's happened in space due to satellites," Dr. James Lowenthal, a professor of astronomy at Smith College in Massachusetts who, in his work, observes young galaxies so distant that their light has traveled billions of years to reach us, told Salon in a video interview. The projected figures are the definition of exponential.

"Now there are over 10,000," Lowenthal said, almost entirely relating to Starlink. But other companies are increasingly vying for real estate in orbit. "There are over 200 projects [in the works], each of them with dozens to tens of thousands of satellites. The Starlink project ... has filed for plans to put in place some 40,000 satellites in low Earth orbit."

Most of the non-SpaceX projects are private companies, too. But governments also want to reclaim their previous dominance of space, and everybody wants in.

"India, China, Brazil are all close behind. The United States military is developing its own [megaconstellations] right now," said Lowenthal. "The nation of Rwanda has filed plans for 330,000 satellites. Whether that comes to fruition or not, it's impossible to predict. But there are hundreds of plans, and the numbers of satellites filed are now at least 500,000 heading towards a million within the next ten years."

These satellites perform valuable services to humans on Earth and even, in some respects, to other living things - for example, by helping us monitor planet-heating emissions. In fact, recent research suggests they will be key to improving our data on CO2 emissions. Dr. John Barentine, an astronomer, dark sky consultant and historian of astronomy in Arizona, even pointed to the background image he uses for video calls as he spoke with Salon: it's a global composite image of Earth made by remote sensing platforms in space. "Without them," he said, "we would not have anything approaching the understanding of the problem that we do have."

But weighing those benefits against the various harms of vast numbers of shiny bodies whirling around the earth is already enough to push dark sky lovers into action. Over the next ten years, our night sky may be irrevocably transformed by the projected legions of satellites.

This affects the casual stargazer, both those of us straining to reconnect with nature on occasional camping trips in the wilderness and those of us who like to look for stars even in the city, longing to see shooting stars or the great spangled expanse of the Milky Way, but making do with a nice bright Venus or Orion's Belt on a clear night.

"What you'll see is the satellites moving across the sky. Those are just reflecting sunlight, just [like] the way the moon is reflecting something. The moon is not shining by itself, it's shining some reflected sunlight. So satellites do the same thing whenever they're in sunlight," Lowenthal explained. The more of them there are, the more shine you'll see. But satellites also shine in two other ways, which laypeople won't notice.
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"One, they actually do have a little bit of their own temperature. They're actually glowing in the infrared. So if you turn a sensitive infrared telescope to them, you see them. They're also emitting radio frequency radiation. That's how they communicate with each other and with the ground by usually short wave, or microwave radiation," Lowenthal said.

This level of interference has been noticeable by radio astronomers for a while. It's manageable for now, but then, the numbers of satellites in the sky are a mere fraction of projected numbers within the next few years.

"I don't think you could talk to a professional astronomer, an observer, who hasn't had satellites go through their images lately," Lowenthal said. "There are papers now, already, that had been published and then retracted, because it turned out that what we thought was a really cool thing was just another satellite."

Such really cool things have included a near-Earth asteroid. "Nope," Lowenthal went on, "it turns out it was that Tesla car that Elon Musk launched into orbit around the sun. That will only happen more often."

Beyond Tesla cars photobombing astronomical images, both amateurs and professionals have been photobombed by numerous non-vehicular Starlink satellites, including an image of the comet Neowise and others. Victims even include the low-orbiting Hubble Space Telescope.

Radiowave interference

The use of the radio spectrum is regulated internationally by the Radiocommunication Sector of the International Telecommunication Union, which publishes regulations allocating frequency ranges for different services or uses such as astronomy, remote sensing, communication and navigation, and also provides thresholds on power flux densities not to be exceeded by other services. The ranges allowed are narrow, far more restrictive than the sort of electromagnetic compatibility standards used on Earth, and unintended electromagnetic radiation can leak from electrical devices and systems on satellites.

For astronomy, the protected range is 150.05 to 153 megahertz. Research published in 2023 showed that emissions measured from dozens of satellites on the Starlink constellation exceeded their intended and allowed thresholds, interfering with the frequencies allocated to radio astronomy. They actually exceeded typical electromagnetic compatibility standards used for commercial electronic devices, too. Now, research published in September showed that the second generation of Starlink satellites also has this problem. And it's 32 times worse.

Blinding light

Satellites aren't currently the main source of light pollution that affects our view of the night sky. But given enough time, they may be - and to a very significant degree. While dark sky advocates have had some success getting individual jurisdictions to begin working towards mitigating the effects of terrestrial light pollution, mitigations are in no way keeping pace with the rate at which low earth orbits are being colonized by these zipping, flashing celestial bodies.

There are working satellites in space, and there are non-functional satellites: what's called space junk or space debris.

It's getting cluttered up there. In fact, the issue of space debris is older than the concern about megaconstellations. Dr. Aparna Venkatesan, an astronomer at the University of San Francisco whose research focuses on cosmology and the re-ionization of the universe after the Big Bang, is a committee co-chair, and Lowenthal and Barentine are committee members, of the Committee to Protect Astronomy and the Space Environment, an advisory committee of the American Astronomical Society. Since 1988, COMPASSE has addressed both ground- and space-based light pollution and radio interference, Lowenthal said, "and the threats attended to use and overuse of space, namely space debris. What happens when things start crashing into each other. And there's just, whenever we do activities in space, there's always some debris associated with it. It's noticeable. Now it's going to get much worse, then what are the effects of it?"

One of those effects can be light. Not only because of especially bright satellites, but just because of their sheer numbers.

"It's like many, many thousands of rotating, glinting ruffled potato chips, basically," as Venkatesan put it. "This glinting, rotating cage of hardware that, first of all, don't cause a streak alone, but are rotating and have a little glint that can throw off a lot of areas of astrophysics, like time domain astrophysics, that look for variable phenomena."

"To their credit," said Lowenthal, "SpaceX has spent millions of dollars on this, and they've had several engineers devoted to this problem."

They've tried things like applying darkening treatments to the satellite. They've tried giving the satellite a visor. They've tried a new coating that is super-dark. But nothing has been enough to solve the problem.

Right after launching, a bunch of satellites heading to join the megaconstellation looks like a string of moving stars going up in the sky. Within a week or so, they reach a higher elevation and are less visible. But they're still not faint enough, despite six years of effort, Lowenthal said.

Additionally, there's the problem of debris from satellites crashing into each other or trash that orbits - everything from droplets of fuel to flecks of paint and other tiny bits of things that float around the Earth at 5 miles (8 km) per second.

"It's a thin haze that reflects sunlight down and makes the sky look artificially bright," Lowenthal said - Venkatesan describes it as a fine dust - noting that some recent research suggests that if debris keeps tracking with the amount of satellites, the night sky as viewed from anywhere on Earth could become several times brighter, perhaps even too bright for astronomical observations to be made at all.

Pollution in space and on land

As well as brightening the sky and interfering with astronomy through their flashes and radio waves, satellites pollute the atmosphere on launch and on re-entry, as research from last October underscored. In 2021, the International Astronomical Union issued a report drafted from the work of 85 scientists that aimed to provide recommendations for how astronomy might be protected from the visible and radio impacts of satellites as well as from terrestrial sources of light through policy changes at local or international levels. When they talk about astronomy, this means that a large part of their focus is on protecting the remote sites where large telescopes and observatories are set up around the world from electromagnetic interference. But it's not just such remote sites that are impacted by satellites, which exert effects on the local and global environment both at launch and at re-entry.

Rockets have long been known to pollute the atmosphere in various ways. Depending on the type of rocket fuel used, launches produce nitrogen oxides, chlorine, black carbon particles, water vapor, carbon monoxide and carbon dioxide - and no propellant avoids creating of some kind of emissions.

The night sky as viewed from anywhere on Earth could become several times brighter, perhaps even too bright for astronomical observations to be made at all.

"There's a lack of policy regarding the environmental impacts of these megaconstellations," Dr. Connor Barker, a research fellow in atmospheric chemistry and physical geography at University College London, told Salon in a video interview. The many satellites now heading up to space don't live long: these days, they're designed to have a five-year lifespan to reduce the amount of trash in orbit. Getting them out of orbit means they re-enter the atmosphere, burning up - but not without a trace. In October, Barker and co-authors Eloise Marais and Jonathan McDowell published a multi-year inventory of air pollutant emissions and CO2 from rocket launches and object re-entries spanning the early growth of the megaconstellation phenomenon from 2020 through 2022.

Such data, he explained, is very challenging to compile. Barker and his team used multiple sources to put together their inventory, crosschecking information they found in different sources against launch livestreams and studies previously conducted by other researchers. Along with gaseous reactive nitrogen, satellites burning up as they re-enter the atmosphere at the end of their lives leave tiny particles of aluminum oxide, imperilling the still-recovering ozone layer. Chlorine (which reacts with the aluminum) and nitrogen oxides also drive ozone depletion.

"We're starting to see that we might be reversing some of the gains we've made from the Montreal Protocol through these increased rocket launch and re-entry rates," Barker said. So reducing debris in space might mean increasing the pollutants in our atmosphere. In fact, it's a bit of a battle of priorities, as Barker explained to Salon. And despite the laudable role satellites play in monitoring greenhouse gas emissions, they contribute to them too.

"We're often dealing with large gaps in the data that we would want," Barker explained. Such gaps make it extremely hard to provide precise information about likely impacts. "For rocket launches, we don't even know sometimes how much fuel is used by the rocket or how much the rocket weighs or what altitudes the rocket operates over. Sometimes we get that information from American or European launch providers. It's extremely hard to get that information for Chinese launches. And then even harder if you're looking at something like North Korea. So there's a real lack of information that having all of that data would make our estimates more accurate."
A SpaceX Falcon 9 rocket carrying a payload of 20 Starlink internet satellites into space soars across the sky after sunset above the Pacific Ocean after launching from Vandenberg Space Force Base on June 18, 2024, as seen from San Diego, California. (Kevin Carter/Getty Images)
The researchers also have not had any direct contact with Starlink, which typically does not provide access to the data they use to make their own estimates and sustainability claims. Salon reached out to Starlink for comment via SpaceX, but did not receive a response.

"It's proprietary, so they don't want another company to take the data. The place you usually get the data from is a user manual - a document used by people that want to launch a satellite, and that will contain details about the rocket," Barker said.

The multiple authors of a December paper published in Nature's Communications Earth and Environment note that "Satellite technologies are essential for global conservation actions through providing continuous, real-time Earth monitoring." The fact that even recent research on the impact of International Dark Sky Places on light pollution relies on observations made from orbiting satellites should make the point. However, the huge increase in rocket launches needed to get all those satellites up there (there were 223 launch attempts in 2023), places a significant and growing strain on the various life forms and biomes where launches take place.

Right around the rocket launch site, local ecosystems are affected by explosive emissions, acoustic oscillations, and land and water use for installation. Meanwhile, the exhaust from rocket boosters and the shuttle cloud itself can cause local damage to vegetation. Fuel spills, chemical leaks, intense noise levels, and acid deposition all lead to loss of local biodiversity - but local in this case means up to 45 km (28 miles) from the launch site. The authors of the Communications Earth and Environment paper cite, for example, research showing hydrochloric acid emitted from solid rocket launches killing fish after it leached into nearby water. They note that over 62% of operating sites are located within or close to protected natural areas.

Falling debris from separating rocket parts extends the affected area to encompass 400 to 1,500 km (249 to 932 miles) from the actual launch site. That's of course not including emissions that become part of the atmosphere and circulate around the globe. And a rocket that blows up can shed debris over huge areas of ocean or land, as demonstrated by a SpaceX test launch that exploded early in March, raining debris over the Caribbean Sea and grounding flights around the globe.

Regulating the skies... And beyond

So far, most efforts to reduce all these effects and their growing impact involves voluntary mitigations, not significant regulation. The main and in fact only legal framework for international space law is the U.N.'s Outer Space Treaty. Article IX states that: "States Parties to the Treaty shall pursue studies of outer space, including the moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extra-terrestrial matter and, where necessary, shall adopt appropriate measures for this purpose."

Two or three problems become evident here. For one thing, this treaty refers to states. Not corporations, not individual billionaires, just states.

"The Outer Space Treaty was really intended to apply to governments," Lowenthal said. "And I don't think the writers of the OST foresaw what we have today, which is essentially something akin to a gold rush or the discovery of oil or the building up of the railroads: tremendous infusion of investment by private interests, also by governments, to help promote the development of a new industry that is seen as potentially an economic driver."

Writing in Northwestern Journal of Law and Policy in 2023, Yuree Nam said that "the space industry and governments have shifted focus away from preventing mass destruction in space. Instead, the space industry is now concerned with private actors commercializing spaceflight and private companies trying to develop commercial activity on Earth and in outer space."

There is other relevant legislation and policy in addition to international space law, of course. But as well as sharing Lowenthal's concerns with the inadequacy of the OST to address the current reality, Nam argues that domestic regulation in the U.S., under the Federal Aviation Administration, is also not up to the job. Though the agency provides licenses to private space companies wishing to launch rockets, environmental review is only a small part of the permitting process. (Satellites being burned up in the atmosphere after five years in orbit is a requirement of FAA licenses under American law.)

Satellites in orbit communicate down to ground stations using radio signals regulated by the Federal Communication Commission. Of course, under the new administration it is possible that much of this will be reorganized. Lowenthal says that an Office of Space Commerce may take over some of the regulatory role of both the FAA and the FCC; all this remains to be seen.

Inadequacy for dealing with private companies is one problem. Another is that the language of the OST refers to avoiding contamination of the moon and other celestial bodies, as well as adverse changes in the environment of the Earth resulting from the introduction of stuff from space. It doesn't refer specifically to all of the issues posed by satellites, including contamination by light, which comes from light-emitting sources on Earth or else from the sun. The sun isn't to blame for light pollution that brightens the night sky, though - we are.

A third potential problem with the language and scope envisioned by the OST is that it doesn't define a geography that captures the creation of light pollution in the night sky, wherever that is exactly, from the perspective of organisms on Earth.

"We think of light pollution as a local issue, and we are lacking a domestic light pollution strategy or a national light pollution policy at present," Venkatesan said. "But even though light pollution can be a local issue, its effects are global."

Not just global, but exponential: the issue of brightening skies, and the other problems of satellites, are both global and growing far more quickly than responses to them in the form of policies, regulations or laws, not to mention monitoring and oversight.

"The challenge with quite so many satellites up there isn't just the changing [atmospheric] chemistry, the sheer numbers, the sheer pace at which they're being launched," noted Venkatesan. "It's that it's happening in parallel with the unchecked firing of a lot of branches of federal agencies that are keeping track of this."

One of the early DOGE layoffs, Venkatesan added, was at NOAA, and involved staff that oversee the traffic coordination system for managing space traffic. Another was in the commercial remote sensing regulatory affairs division, affecting the staff responsible for oversight of remote sensing from space that allows us to understand the scale of the problem of light pollution down on Earth.

"We are not fundamentally opposed to the development of space," Barentine told Salon. "What we are concerned about is the way that it's proceeding."

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Here’s what to expect from Project Kuiper’s first full-scale satellite launch

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Here’s what to expect from Project Kuiper’s first full-scale satellite launch

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Here’s what to expect from Project Kuiper’s first full-scale satellite launch

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United Launch Alliance will send 27 Kuiper satellites into low Earth orbit as we begin a full-scale deployment of our satellite internet network.

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Why We Need Dark Skies: The Impact of Light Pollution on Planetary Health

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Why We Need Dark Skies: The Impact of Light Pollution on Planetary Health

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Why We Need Dark Skies: The Impact of Light Pollution on Planetary Health

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In this webcast, Tim Brothers, manager of the MIT Wallace Astrophysical Observatory and Vice President of the Massachusetts chapter of the International Dark Sky Association discusses light pollution, explains the solutions that are immediately on hand, and what you can do to help.

Light pollution is one of the fastest growing environmental problems, because it negatively impacts our nighttime environment, our climate, and the health of humans, animals, and plants. Here are some of the topics that Tim Brothers will discuss:

* Wasted light means wasted energy, which means greater greenhouse gas emissions
* LED lights are more energy efficient, but they create more blue light and sky glow
* Artificial lighting disrupts ecosystems and human health
* Local legislative and town efforts that you can support
* How individual homeowners can make a difference

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New How-to-guide: Protecting nocturnal pollinators " All-Ireland Pollinator Plan

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The All-Ireland Pollinator Plan is delighted to release a new free resource on protecting nocturnal pollinators. We produced this new guide in collaboration with Georgia MacMillan of the Mayo Dark Sky Park and Rachel McKenna & Michael O'Donnell of MothsIreland. ... Continued

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Working the Night Shift: Glacier’s First Nocturnal Pollinator Bioblitz (U.S. National Park Service)

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Working the Night Shift: Glacier’s First Nocturnal Pollinator Bioblitz (U.S. National Park Service)

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Working the Night Shift: Glacier’s First Nocturnal Pollinator Bioblitz (U.S. National Park Service)

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Nocturnal pollination: an overlooked ecosystem service vulnerable to environmental change

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Nocturnal pollination: an overlooked ecosystem service vulnerable to environmental change

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Author links open overlay panel

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Researchers stunned by behavior shift in unique fish species: ‘Need for more comprehensive research’

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Researchers stunned by behavior shift in unique fish species: ‘Need for more comprehensive research’

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Researchers stunned by behavior shift in unique fish species: ‘Need for more comprehensive research’

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A new study shows that Prozac and other chemicals could have a major impact on fish behavior in urban environments.

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DarkSky designation can mitigate ‘privatisation of celestial sphere’

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DarkSky designation can mitigate ‘privatisation of celestial sphere’

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DarkSky designation can mitigate ‘privatisation of celestial sphere’

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From the University of Auckland – Analysis: The expansion of satellite activity has, in part, led to the increased push by certain communities to seek DarkSky certification

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Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

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Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

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Abstract

The present review draws together wide-ranging studies performed over the last decades that catalogue the effects of artificial-light-at-night (ALAN) upon living species and their environment. We provide an overview of the tremendous variety of light-detection strategies which have evolved in living organisms - unicellular, plants and animals, covering chloroplasts (plants), and the plethora of ocular and extra-ocular organs (animals). We describe the visual pigments which permit photo-detection, paying attention to their spectral characteristics, which extend from the ultraviolet into infrared. We discuss how organisms use light information in a way crucial for their development, growth and survival: phototropism, phototaxis, photoperiodism, and synchronization of circadian clocks. These aspects are treated in depth, as their perturbation underlies much of the disruptive effects of ALAN. The review goes into detail on circadian networks in living organisms, since these fundamental features are of critical importance in regulating the interface between environment and body. Especially, hormonal synthesis and secretion are often under circadian and circannual control, hence perturbation of the clock will lead to hormonal imbalance. The review addresses how the ubiquitous introduction of light-emitting diode technology may exacerbate, or in some cases reduce, the generalized ever-increasing light pollution. Numerous examples are given of how widespread exposure to ALAN is perturbing many aspects of plant and animal behaviour and survival: foraging, orientation, migration, seasonal reproduction, colonization and more. We examine the potential problems at the level of individual species and populations and extend the debate to the consequences for ecosystems. We stress, through a few examples, the synergistic harmful effects resulting from the impacts of ALAN combined with other anthropogenic pressures, which often impact the neuroendocrine loops in vertebrates. The article concludes by debating how these anthropogenic changes could be mitigated by more reasonable use of available technology - for example by restricting illumination to more essential areas and hours, directing lighting to avoid wasteful radiation and selecting spectral emissions, to reduce impact on circadian clocks. We end by discussing how society should take into account the potentially major consequences that ALAN has on the natural world and the repercussions for ongoing human health and welfare.

Keywords: artificial-light-at-night, light-emitting-diodes, photoreception, biological clocks, ecosystems, anthropogenic impact

Introduction

Human activities are almost exclusively associated with brightly lit environments. The last century has seen an unprecedented increase in the use of Artificial Light at Night (ALAN), with a current ongoing global increase rate of more than 6% per year ( Hölker et al., 2010). This is dramatically affecting land as well as aquatic and open sea areas. Mediterranean and temperate zones, mangroves and forest regions in proximity to agricultural areas are particularly affected ( Votsi et al., 2017). Today, more than 80% of the worlds population lives under a "lit sky" at night ( Falchi et al., 2016), actually affecting up to 99% in Europe and North America and on the increase in the Middle East ( Tamir et al., 2017) and Asia ( Jiang et al., 2017). ALAN acts both directly and indirectly (through sky glow) upon organisms. The illuminance at ground level can equal that of the full moon (0.01<<1 lx) ( Bennie et al., 2015a, 2016; Figure 1) and can even be amplified by the cloud ceiling. ALAN was first intended to detect obstacles, increase road safety and secure potentially dangerous areas at night, but has now been extended to all aspects of human activities, including industrial, commercial, amenity spaces or tourist purposes. Illumination levels often exceed real needs; in some areas the aesthetic aspects (lighting of monuments) or advertising (lighting of commercial areas, shop windows, street signs and illuminated posters) have been given precedent. It follows that untouched natural areas - essential to the development of wildlife - are constantly decreasing. The consequences on biotopes and living organisms (including humans) are multiple. Basic responses and functions related to orientation in space (phototaxis, phototropism) and time (circadian rhythms) are affected by ALAN. These processes are the result of millions of years of evolution, while ALAN-induced changes are operating on a time scale of only a few decades. This is particularly evident when it comes to temporal events, which depend on the predictable alternation of light (L) and darkness (D) during the 24 h LD cycle, day after day and season after season. From the very earliest times of life on earth, organisms developed time-measurement systems - circadian clocks - which allowed them to forecast and anticipate these natural changes, essential for aligning physiological activity with the appropriate time. As a result, most of the basic functions of living organisms are controlled by these internal, genetically determined, clocks. These clocks depend absolutely on the 24 h LD cycle to accurately synchronize their activity with solar time, and in turn they orchestrate a myriad of downstream biochemical, physiological and behavioural events so that the right process occurs at the right time. Thus, changing the natural LD cycle cannot be without consequences for biological organisms. In humans, perturbation of the circadian system results in major physiological impacts ( Attia et al., 2019), for example in altered hormonal balance, including melatonin secretion. Melatonin is one key circadian clock output involved in the synchronization of many rhythmic functions; in addition it is suspected to possess powerful anti-oxidative properties ( Reiter et al., 1997). In humans, a correlation between ALAN and the appearance of various disorders (activity/sleep rhythms, mental health disorders, energy metabolism, weight gain and obesity, sensitivity to some cancers [breast, prostate]) has been documented quite extensively ( Dominoni et al., 2016; Attia et al., 2019) but the level of proof remains low because in most cases the light intensities used are far above the levels encountered in ALAN.

FIGURE 1.

(A) Illuminance measured in the horizontal plane from a typical street light (Phillips Cosmopolis, metal halide lamp). The illuminance level decays rapidly with distance to the lamp. (B) Comparison of measured illuminance from natural sources of light to artificial light sources - axis is on a logarithmic scale, and bars present approximate ranges based on field measurements. From Bennie et al. (2016). No special permission required.

Here, we provide an overview of the tremendous variety of light-detection strategies which have evolved in unicellular organisms, plants and animals. We further give a comprehensive description of the different visual pigments which permit photo-detection in all living organisms from ultraviolet to infrared. The review then moves on to discuss how living organisms actually use light information in a meaningful way, crucial for their development, growth and survival: phototropism, phototaxis, photoperiodism, and synchronization of circadian clocks. These aspects are treated in depth, as their perturbation underlies much of the potentially disruptive effects of ALAN. The review goes into considerable detail on circadian networks in living organisms, since these fundamental features exist in virtually all life forms and are of critical importance in regulating the interface between environment and body. It is necessary to understand the diverse principles underlying their functioning across the different phyla in order to appreciate why ALAN can represent such a disruptive influence. Although much of the data reported in the literature necessarily comes from older lighting technology, the review addresses how the approaching ubiquitous introduction of light-emitting diode (LED) technology may exacerbate, or in some cases reduce, the generalized ever-increasing light pollution. A focus is put on the fundamental role of short wavelength emissions, since these are the most relevant wavelengths when considering signalling through vertebrate photoreceptive tissues and synchronization of central circadian clocks. Nevertheless the paper also stresses that due to the huge range of light detection systems used by living organisms, other wavelengths may also be problematic. Numerous examples are given of how widespread exposure to ALAN is perturbing many aspects of plant and animal behaviour and survival. We examine the potential problems at the level of individual species and populations before extending the debate to the consequences for integrated ecosystems. It also emphasizes additive harmful effects resulting from the impacts of ALAN together with other anthropogenic pressures. The article concludes by debating how these anthropogenic changes could be easily mitigated by more reasonable use of available technology and how society should take into account the potentially major consequences that ALAN has on the natural world and the repercussions for ongoing human health and welfare.

The Integration of the Light Signal in Living Organisms

Nothing in biology makes sense except in the light of evolution (Dobzhansky cited in Lamb, 2013).

The capture of light information goes back to ancestral cyanobacteria, the first known representatives of life on earth, which appeared ∼3.8 billion years ago. It allows organisms to orientate in space (phototropism for animals, phototaxy for plants) and time (synchronization of the endogenous clocks that drive the daily, lunar and annual rhythms of metabolic, physiological and behavioural functions). Living beings have implemented a huge variety of systems and mechanisms in order to capture light, from simple photoreceptive organelles to highly complex structures such as the chloroplast of plants and the camera eyes of vertebrates, insects and cephalopods.

In unicellular organisms, photoreception is mediated by a photoreceptor organelle existing as either a single spot (cyanobacteria, euglena) or a more elaborated structure (dinoflagellates), containing all the elements found in a vertebrate eye, i.e., pigment, a cornea-shaped surface, a lens and a lamellar structure ( Gehring, 2005, 2011, 2014). It has been hypothesized that these organelles might correspond to chloroplasts incorporated by horizontal transmission, but having lost their photosynthetic activity ( Gehring, 2012).

Cyanophyceae, the current representatives of the ancestral cyanobacteria are, like the original form, capable of capturing light and ensuring photosynthesis. They exist as single cell units or associated in filaments, and can fix carbon dioxide [CO ₂] and release oxygen [O ₂], but have no chloroplast. Phototaxy and photoperiodic synchronization of circadian clocks have been demonstrated in Cyanobacteria ( Gehring, 2012), as in the terrestrial Cyanobacterium Leptolyngbya sp., which shows two maxima of absorption (λmax) at 456 and 504 nm. Populations of Cyanobacteria are increasing worldwide, favoured by trophic and/or ecological imbalances (including eutrophication of water), and pose major physical (invasion, obstructions) and toxicological (production of dangerous or even deadly toxins) problems ( Svrcek and Smith, 2004).

The Chloroplast of Plants

The ingestion of cyanobacteria by primitive eukaryotic cells ∼1.5/1.6 billion years ago led to the formation of chloroplasts ( Figure 2), found in the cytoplasm of eukaryotic photosynthetic cells ( Kirchhoff, 2019). In the unicellular alga of the Chlamydomonas genus, there is one chloroplast per cell, while multicellular plants possess several tens of chloroplasts in one cell, with the leaves showing the highest density. The chloroplast allows photosynthesis, i.e., it absorbs light energy to fix inorganic CO ₂ and produces glucose and O ₂ (the highest production of O ₂ is from algae and marine phytoplankton, followed by forests). Moreover, it is involved, by interacting with photoreceptive molecules and circadian clock genes, in the response to light ( Jaubert et al., 2017).

FIGURE 2.

The chloroplast of plants and photosynthetic algae absorbs basic elements and uses sunlight to produce sugar and other organic molecules to fulfil their needs ( Kirchhoff, 2019) @JackFalcón.

The Photoreceptive Cells and Organs of Animals

The rhabdomeric and ciliary photoreceptors are the two main types of photoreceptive cells found in the animal kingdom. Both show a highly segmented and polarized organization, with a photoreceptive pole made of folds or stacks of membrane, a cell body and an opposing pole for neurotransmission ( Figure 3A). Evolution of photoreceptor cells and organs runs in parallel, and studies have shown that eyes and other photoreceptive structures have a monophyletic origin that started with a single prototype ( Fain et al., 2010; Gehring, 2012; Lamb, 2013; Gavelis et al., 2015). Evolution led to the appearance of a variety of complex ocular types ( Figure 3B). Thus, while the camera-type eye containing ciliary photoreceptors characterizes the eyes of humans and other vertebrates, camera-type eyes are also found in jellyfish and cephalopods, which instead possess rhabdomeric photoreceptors as is the case in most invertebrates. However, coexistence of rhabdomeric and ciliary photoreceptors is not uncommon, as observed in the cephalochordate Amphioxus, the living proxy of all vertebrates ( Zhang Q. L. et al., 2019). The retina of the hagfish eye, as well as the pineal gland of fish, frogs and sauropsids, is composed mainly of photoreceptor cells connected directly to ganglion cells. The first are of the ciliary type and the second are derived from rhabdomeric photoreceptors, as shown at least in the hagfish ( Autrum et al., 2012; Lamb et al., 2007; Lamb, 2013). The retina of all other vertebrates has become more complex, with the appearance of bipolar, horizontal and amacrine cells in an intermediate position. The most recent data indicate that bipolar cells are derived from ciliary type photoreceptors, while the ganglion cells derive from the rhabdomeric line; amacrine and horizontal cells would also belong to the rhabdomeric line ( Lamb, 2013).

FIGURE 3.

(A) Rhabdomeric microvilli-based (invertebrates) and cilia-based (vertebrates) photoreceptors display conserved cell polarity and topology. They evolved most probably from a common ancestor in early Bilateria. The photosensory pole is made of stacks of plasma membrane separated from the baso-lateral membrane by a zonula adherens. N, nucleus. (B) The main optical designs of eyes: (a) The pinhole eye; light (yellow arrow) falls directly upon the photoreceptors (brown layer). (b) The concave-mirror eye; light crosses the retina, and is then focused back onto the retina upon reflection from a hemispheric reflective mirror ( tapetum, grey zone). (c) The camera type eye; light is focused by the lens to form an image on the retina. (d and e) The compound eyes; light reaches the photoreceptors exclusively from the small corneal lens (d type) located directly above, or focused through a large number of corneal facets and cones to be directed towards single rhabdoms (e type). Redrawn from Warrant (2019).

Compound and Camera Type Eyes

A dozen different eye structures have been identified in animals, which developed through different evolutionary pathways (divergent, parallel, or convergent) ( Shubin et al., 2009). Some are just scattered photoreceptors (alone or a few together) all along the body, found in small invertebrates and in larvae of insects and worms. They are designated as primitive eyes because they are associated with a pigmented cell positioned on one side, permitting the perception of light directionality. These structures are simple dosimeters of the surrounding light intensity allowing negative or positive phototaxy (escape or attractive behaviour respectively). In tubular worms these groups of cells form wells or pit eyes; the pit eye forms a small hollow in which photoreceptor cells display different orientations, thus allowing spatial detection of light ( Figure 3Ba). From these pit eyes appeared the spherical concave mirror eyes with a pupil, but without a crystalline lens, as seen bordering the mantle of the bivalves (clams, scallops) ( Figure 3Bb). More elaborated camera eyes are found in vertebrates, molluscs (squid, octopus), jellyfish, some annelids, arthropods (including spiders), insect larvae and copepods ( Figure 3Bc). Finally, the compound eye, the most widespread model, is characteristic of insects (75% of existing animal species), most crustaceans, myriapods, some bivalves and polychaetes ( Figure 3Bd,e). Compound eyes are formed of identical units called ommatidia, which each contains a cluster of photoreceptor cells surrounded by supporting cells and pigmented cells. Each ommatidium possesses a cornea and a conical lens that focuses light towards the rhabdomeric photoreceptors. In the majority of diurnal species, each ommatidium is isolated from its neighbours by a pigment layer, which makes communication between them impossible ( Figure 3Bd). In nocturnal species the absence of pigment allows the diffusion of light from one ommatidium to its close neighbours, conferring a gain of sensitivity ( Figure 3Be).

The eye with its retina is not the only structure that allows light detection, as both invertebrates and vertebrates possess additional extra-retinal light sensitive structures.

Extraretinal Photoreception in Vertebrates

Aquatic vertebrates, amphibians and lizards possess a pineal complex formed by a pineal gland associated with either a parapineal organ or a parietal eye (depending on the species) ( Collin et al., 1988; Falcón, 1999; Figures 4A-J). The gland appears as an evagination of the roof of the diencephalon, located at the surface of the brain. In the majority of cases (particularly in poikilothermic species) the skull directly above the pineal gland is thinner and translucent and the skin is less pigmented ( Figures 4A-D). In large fish ( e.g., the tuna) where the brain is located deep inside the head, a translucent cartilaginous tube directs light from the surface to the pineal gland (personal observations). All these anatomical characteristics allow better light penetration. In addition to the pineal gland, frogs and lizards possess a parietal eye ( Figures 4E-J) located between the skull and the skin, which sends a nerve that crosses the skull to reach the brain. In addition, the parietal eye of lizards possesses a lens ( Figure 4J). In birds, snakes and mammals these specializations have regressed: the pineal gland of adult mammals is often located more deeply in the brain and has lost its ability to detect light directly, even though they still express the proteins necessary for phototransduction ( Figures 4K,L). Furthermore, during development mammalian pinealocytes display morphological features characteristic of ciliary photoreceptor cells but which subsequently regress ( Blackshaw and Snyder, 1997).

FIGURE 4.

Extraretinal photoreception in vertebrates. ( A) Dorsal view of the head of the Polar Cod Boreogadus saida; the pineal organ (PO) is located in the sagittal axis just behind the eyes in an area with unpigmented meninges (@JackFalcón). ( B) Dorsal view of the brains of the Red Mullet Mullus surmulletus showing the location of the pineal organ (thick arrow), located in between the two cerebral hemispheres (Ch); OT, optic tectum; Cer, cerebellum; from Baudelot (1883) (no permission required). ( C) Schematic sagittal sections through the epithalamus area of, from top to bottom, lampreys, chondrichtyens and teleost fish; from Studnicka (1905). Note that the skull above the pineal organ is thinner, as also seen in panel (D) (no permission required). The histological sagittal section is from the Sea Bream Sparus aurata; the pineal is located in a kind of large pit below the skull (note that the tegument above also appears thinner) (gift from Professor J.A. Muñoz Cueto, Cadiz, Spain). ( E,F) Head dorsal views showing the spot position of the frontal organ in the American Bullfrog Rana catesbeiana ( E) and the parietal eye of the Zebra-tailed Lizard Callisaurus draconoides ( F) (arrows) (@JackFalcón). ( G,H) Schematic sagittal sections through the epithalamus areas of frogs ( G) and lizards ( H); the pineal organs are located below the skull, while the frontal/parietal eyes are located in the skin connected to the brain by a stalk ( Studnicka, 1905) (no permission required). (I) Dorsal fossil skull of the ancestral amphibian Thoosuchus jakovlevi showing the location of the frontal organ hole just equidistant from the eyes (with permission from https://commons.wikimedia.org/wiki/File:Thoosuchus_jakovlevi.JPG). ( J) The pineal eye of the tuatara Sphenodon punctatus resembles a simplified retina with an eye cup and a lens-like structure; sagittal section from Dendy (1911) (no permission required). ( K) In the avian brain the pineal organ form a gland in between the cerebral hemispheres and the cerebellum (gift from Professor J.P. Collin). ( L) In humans the gland is located deep in the brain (@JackFalcón).

The pineal epithelium of non-mammalian vertebrates displays the characteristics of a simplified retina as it contains cone-type photoreceptors connected to ganglion cells, the latter sending their axons towards specific brain centres. It is of interest to note that retinal and pineal brain projections overlap in some areas, thus providing convergent light information ( Ekström and Meissl, 2003). In contrast to the retina, the pineal organ is only a dosimeter of light intensity, albeit of great sensitivity. In addition to this nervous information pineal photoreceptors also produce the " time-keeping hormone" melatonin (see Localization of the Circadian System - Vertebrates) ( Falcón, 1999). In the course of evolution snakes and mammals have lost the parapineal and parietal organs, as well as the direct photosensitivity of the pineal gland, and they no longer produce nervous information ( Collin et al., 1988). In these species, the pineal cells (pinealocytes), receive light information via the retina and a complex nerve pathway; only the nocturnal production of melatonin persists ( Klein et al., 1997). Birds display features characteristic of both early and late vertebrates.

In addition to these organized photoreceptive organs, intracerebral photoreceptors, the existence of which had been postulated early in the last century ( Von Frisch, 1911; Benoit and Assenmacher, 1954), have been found in fish, lizards and birds ( Hang et al., 2016; Haas et al., 2017) (see also below Figure 11). Their role remains enigmatic; some may contribute to the annual control of reproduction ( Benoit and Assenmacher, 1954).

FIGURE 11.

Schematic representation of the photoneuroendocrine organization in the non-mammalian brain. The drawing pictures a frontal section of the brain diencephalic area. Light information is captured by the lateral eyes and the pineal organ. Photosensitive units, expressing different types of opsins, have also been identified along the 3rd ventricle (3rd V; yellow and green circles). Major circadian clock machineries are present in the pineal and retinal photoreceptors as well as in the basal diencephalon (preoptic area [POA] and suprachiasmatic nuclei [SCN]) of lizards and birds. The pineal gland of fish and lizards also integrates temperature information from the external environment. The concomitant action of light, temperature and other internal factors, shapes the rhythmic nervous (blue) and hormonal (red; melatonin) outputs (see text for details), providing a temporal message transmitted to the neuroendocrine axis and downstream targets (peripheral endocrine organs). Melatonin acts through specific receptors (stars) distributed in different tissues and organs. While the main retinal output subserves visual function, a few other fibres also terminate in different parts of the basal diencephalon, where some converge with fibres originating from the pineal gland. Some of the targeted areas also express melatonin receptors. This double or triple input contributes to synchronizing the neuronal activity of the basal diencephalon. In sauropsids the POA and SCN neurons also relay retinal information to the pineal gland. The entire neuroendocrine axis is targeted by ALAN together with multiple other disruptors including temperature rises and pollutants [ e.g., endocrine disruptors] acting directly or indirectly at different levels of the loop.

Finally, ectothermic vertebrates (fish, amphibians, and lizards) possess photosensitive cells on the surface of their skin, which participate in the control of migration in lampreys ( Binder and McDonald, 2008), the aggregation/dispersion of skin pigments in fish and frogs ( Moriya et al., 1996; Chen et al., 2014), or basking in reptiles ( Tosini and Avery, 1996).

Extra-Retinal Photosensitivity in Invertebrates

In addition to their rhabdomeric eyes, insects possess ocelli and eyelets, which may have various shapes and locations ( Figures 5A-E). The ocelli of insects are simple lens eyes consisting of a single, large aperture lens, followed by several hundreds of rhabdomeric photoreceptors which converge onto a few tens of interneurons ( Berry et al., 2011). Drosophila eyelets contain 4 to 6 rhabdomeric photoreceptors and are derived from the larvae visual organs ( Helfrich-Förster et al., 2002). Compound eyes and ocelli have a common ancestral origin ( Friedrich, 2006), and these extra-retinal photoreceptors are likely to be involved in behaviour and synchronization of endogenous rhythms. Spiders do not have ocelli, but may possess from 1 to 4 pairs of eyes with different functions ( Figure 5F)

FIGURE 5.

Extra-ocular light perception in various insect species (A-E) and eyes of a spider (F). Arrows point to ocellar structures as found in Netelia sp.(A), Heptagenia sp.(B), grasshopper Locusta migratoria(C), Eristalinus sepulchralis(D), Vespa cabro(E), and Philodromus dispar(F). Photo credits: P. Falatico ( A,B,D,E; @ http://aramel.free.fr/), J Falcón (C), D. Vaudoré ( F; @ https://www.galerie-insecte.org/galerie/ref-183890.htm). No special permissions required.

Photopigments and Visual Perception

Phytochromes

Phytochromes are found in plants, fungi, bacteria and cyanobacteria, unicellular algae and diatoms. They are covalently associated with a phytochromobilin as chromophore in plants and cyanobacteria, and biliverdin in other bacteria and fungi ( Bhoo et al., 2001; Glukhova et al., 2014; Huche-Thelier et al., 2016). In plants, several forms of phytochromes may be present simultaneously (five in Arabidopsis thaliana, three in sorghum, black cottonwood and rice, and two in pea) ( Demotes-Mainard et al., 2016). They display maximal sensitivity in the red range of wavelengths, although response to other wavelengths is also observed but with much lower sensitivity ( Figure 6A). Phytochromes exists in two states: the inactive state has a sensitivity maximum in the red (580 < λmax < 660), while the active state displays its maximum in the infrared (690 < λmax < 720). The final effects on downstream regulated processes in the plant depend on the red/infrared ratio ( Bhoo et al., 2001; Demotes-Mainard et al., 2016). Light induces bilin photoisomerization and triggers photoconversion from the red to infrared form, prompting activation of the phytochrome HIS-kinase activity and downstream cascades. Darkness induces the opposite and thus the plant needs a dark phase to regenerate the phytochrome from the infrared to red form. Consequently, a natural LD 24 h cycle is essential for the proper synchronization and regulation of physiological cycles in plants (see below).

FIGURE 6.

(A) The spectral sensitivity of plants. See text and ( Huche-Thelier et al., 2016) for details. ( B) Different states of the flavoquinone cofactor of Cry and corresponding photosensitivity (see text for details). (C) Phylogenetic tree of the photolyase/cryptochrome family. Modified from Du et al. (2014), with permission.

It is of interest to note that phytochromes also contribute to blue light-dependent regulation either redundantly or synergistically with cryptochromes (Cry; the blue light photoreceptors), and that physical interactions between Cry and phytochromes proteins have been demonstrated ( Demotes-Mainard et al., 2016).

Cryptochromes

Cry are found in all living organisms ( Chaves et al., 2011; Yu and Fischer, 2018). They belong to the photolyase family of proteins and use flavin adenine dinucleotide (FAD) as a cofactor ( Figures 6B,C). Photolyases and Cry from the DASH (for Drosophila, Arabidopsis, Synechocystis, Human) family (Cry-DASH) are involved in DNA repair ( Tagua et al., 2015), which operates between 350 and 530 nm. In plants and animals Cry1 and Cry2 have lost the DNA repairing property. UV-A (λmax 370 nm) and blue (λmax 450 nm) radiations activate an electron transfer and reduction of FAD (initially in an oxidized form) ( Huche-Thelier et al., 2016; Liu et al., 2016; Figure 6C). In the animal kingdom Cry are also part of the circadian clock molecular machinery, i.e., they ensure both the capture of the light signal (input to the clock) and the function of the clock itself. However, this is not the case in vertebrates where they are no longer light sensitive (see section "Orientation in Time: The Circadian Clocks" below).

As mentioned above, Cry interact with phytochromes in plants, where they also regulate phototropin expression (see section "LOV (Light, Oxygen, or Voltage) Domain Proteins"). They are also involved in the mechanisms of orientation (insects) and magnetoreception (plants, insects, birds) ( Chaves et al., 2011; Gehring, 2012). For example, strong magnetic fields reduce plant growth in blue light but not in red light. In Cry deficient ( Cry−/−) Drosophila ( Drosophila melanogaster) and cockroaches ( Periplaneta americana), magnetic field orientation function is lost while it is restored in transgenic animals expressing the human gene ( Cry2+/+) ( Bazalova et al., 2016). Similarly, magnetic field orientation through retinal Cry has been demonstrated in migratory birds (particularly nocturnal migrants) and, under dim light intensity, orientation remains correct only at wavelengths under 530 nm ( Mouritsen et al., 2004a, b; Solov'yov et al., 2010; Niessner et al., 2011; Fusani et al., 2014).

LOV (Light, Oxygen, or Voltage) Domain Proteins

Light, oxygen, or voltage domain containing proteins are a family of blue light receptor proteins that include phototropins, ZTL/FKF1/LKP2 and aureochromes ( Suetsugu and Wada, 2013). Phototropins are specific to green plants (land plants and green algae) and ZTL/FKF1/LKP2 to land plants. Aureochromes are specific to photosynthetic stramenopiles, including yellow-green algae ( Xanthophyceae), brown algae ( Phaeophyceae), and diatoms ( Bacillariophyceae).

Phototropins are serine/threonine kinase proteins, which are sensitive to blue and UV-A light ( Figure 6A). They use mono-nucleotide flavin (FMN) as chromophore. Studies in A. thaliana have demonstrated that phototropin expression is regulated by phytochromes and Cry ( Huche-Thelier et al., 2016). Phototropins are involved in the control of phototropic responses (hypocotyl and stem bending, and leaf positioning), the accumulation of chloroplasts and opening of the stomata (responsible for gaseous exchanges between the plant and its environment) ( Huche-Thelier et al., 2016).

Like the phototropins, ZTL (Zeitlupe), FKF1 (Flavin-binding Kelch), and LKP2 (LOV Kelch Protein-2) are also associated with FMN and responsive to blue and UV-A wavelengths ( Figure 6A; Suetsugu and Wada, 2013). ZTL regulates the circadian clock either directly (through degradation of key clock proteins) but also can indirectly affect the flowering time. LKP2 and FKF1 predominantly control photoperiodic flowering (scent emission, corolla opening, and movements), the former through regulating the circadian clock, and the latter acting downstream of the clock; studies also suggest they contribute to controlling hypocotyl growth ( Imaizumi et al., 2003; Dodd et al., 2015; Yon et al., 2016). In fungi, the blue photoreceptor proteins White Collar-1 (WC1) and Vivid (VVD), two LOV domain-containing photoreceptors, are part of the circadian clock machinery ( Hurley et al., 2015; Yu and Fischer, 2018; Saini C. et al., 2019).

Opsins

Opsins are members of the G-protein-coupled 7 transmembrane domain receptor (GPCR) superfamily that are associated with the chromophore retinal. This feature is a fundamental distinction between opsins and phytochromes, Cry and LOV-domain containing proteins, which are cytosolic. Upon illumination, retinal isomerizes from the 11- cis to all- trans configuration (in vertebrates), or all- trans to 13- cis (in bacteriorhodopsin), triggering the cellular response to light ( Shichida and Matsuyama, 2009). Opsins, evolved from a common ancestral molecule ∼ 700 million years ago ( Figure 7), show enormous diversity in structure, tissue distribution and function ( Porter et al., 2012); more than 1000 sequences are available ( Shichida and Matsuyama, 2009). The two categories, microbial (type I) and animal (type II) opsins, share a common architecture but with little sequence homology and have different functions ( Kandori, 2015).

FIGURE 7.

The family of opsins in the tree of evolution. C-opsin family includes the vertebrates visual and brain opsins (Rh1, Rh2, SWS1, SWS2, M/LWS, pinopsins, parapinopsins, vertebrate ancient and parietal opsins), the chordates' brain opsins (teleost multiple tissue opsins (TMTs), encephalopsins and uncharacterized amphioxus and urchin opsins), the arthropod opsins (honeybee ptersopsin, and uncharacterized insect and Daphnia pulex opsins), and the annelids group (uncharacterized Platynereis brain and urchin opsins). Cnidops family includes ctenophore and cnidiarian opsins. R-type opsins include the arthropod visual pigments (M, LWS, and SWS), the annelid, Platyhelminthes and mollusc visual pigments, the melanopsins (vertebrates' melanopsin 1 and 2, and amphioxus sequences) and uncharacterized tunicate, amphioxus and mollusc opsins. Group 4 Opsins include neuropsins (four separate clades), amphioxus, sea urchin and scallop opsins, RGR (uncharacterized mollusc opsins) and peropsins (amphioxus and hemichordate opsins). See text and ( Porter et al., 2012) for more details. Modified from Porter et al. (2012). No special permission required.

FIGURE 8.

Spectral sensitivity curves of selected vertebrate and invertebrate representatives, illustrating the wide variety of light detection systems encountered. Vertebrates: human Homo sapiens, mouse Mus musculus, chicken Gallus domesticus, Salamander Salamandra, goldfish Carassius auratus. Invertebrates: elephant hawk moth Deilephila elpenor, dragonfly Hemicordulia tau, butterfly Papil io xuthus, annelid worm Torr ea candida, nocturnal spider Cupiennius salei. Adapted and modified from Imamoto and Shichida (2014), Warrant (2019).

FIGURE 9.

(A) Penetration of light into the water column and (B) illustration of the depth at which different colours of light penetrate ocean waters. ( B is modified from the NOAA Office of Ocean Exploration and Research, with permission).

Orientation in Space: Phototaxis, Phototropism

Orientation in space, defined as phototaxis in animals and phototropism in plants, are movements in response to the lighting environment. Positive and negative phototaxis ( i.e., towards or away from the light stimulus) is most often triggered by blue light detection, but not only ( Randel and Jekely, 2016). It may cover the whole spectrum, from UV/A up to near-infrared (Cyanobacteria, Chau et al., 2017; Wilde and Mullineaux, 2017) or just part of it (UV to green in the fruit fly Drosophila melanogaster larvae, Humberg and Sprecher, 2017); UV/blue in Hemiptera Diaphorina citri ( Paris et al., 2017); near-infrared in the zebrafish Danio rerio larvae ( Hartmann et al., 2018); and green in the bat Pipistrellus nathusii ( Voigt et al., 2017). Animals (particularly aquatic larvae) may change their preferences during development.

Phototropism characterizes plants and fungi, which, as sedentary organisms, have evolved the ability to alter their growth to optimize light capture and photosynthesis ( Goyal et al., 2013; Fankhauser and Christie, 2015; Schumacher, 2017). In most plants and fungi phototropism is triggered by both red and UV-A/blue light, while in flowering plants blue light is the predominant signal. In Botrytis cinerea, a pathogenic fungus of plants, light stimulates germination of the conidia, while dark stimulates its growth. Also, germ tube growth is reduced by near-UV, blue and far-red light, which induce negative phototropism, while red light promotes germ tube elongation and induces positive phototropism ( Schumacher, 2017). In fact, negative phototropism induced by near-UV/blue light increases pathogenicity, whereas positive phototropism induced by red light suppresses it.

Orientation in Time: The Circadian Clocks

Orientation in time is provided by the so-called circadian system. This system is made of circadian clocks, which function autonomously and rhythmically with a period of approximately 24 h ( Bell-Pedersen et al., 2005). Circadian clocks are present in virtually all living organisms, including cyanobacteria, micro-green algae, plants, fungi and animals ( Figure 10). The alternation of light and dark during the 24 h LD cycle is the main environmental input signal to the clocks (although there are others such as food intake, temperature or social interaction), synchronizing and entraining their autonomous activity with the natural world. In return, the clocks produce a number of rhythmic messages, either through direct gene regulation (so-called clock-controlled genes or ccg) or indirectly through activating second messenger cascades. Together, the rhythmic input to the clocks, the clocks themselves and their rhythmic outputs, constitute the circadian system. Such an organization governs myriad metabolic, physiological and behavioural processes, thereby synchronizing their activities with the natural periodicities ( Reiter, 1991; Falcón et al., 2007b, 2010; Bloch et al., 2013; Table 1). It has been estimated that between 10 and 20% of the genome shows a circadian expression (about 3,000 genes in humans), while a recent study of non-human primates showed that >80% of de novo transcripts were rhythmic (possibly under circadian control but also possibly evoked by the light-dark cycle or the sleep-wake cycle) ( Mure et al., 2018).

FIGURE 10.

Simplified schematic representation of the circadian clock in (A) mammals, (B) insects, (C) Cyanobacteria, (D) fungi, and (E) plants. For details see Saini R. et al. (2019). Abbreviations: CCA1, circadian clock associated 1; CCG, clock controlled genes; Clk, clock; CRY, cryptochrome; CYC, cycle; ELF, early flowering; FRH, FRQ-interacting RNA, helicase; FRQ, frequency; GI, gigantea; LHY, late elongated hypocotyl; LUX, lux arrhythmo; PER, period; Rev-Erbβ (orphan nuclear receptor family 1); PRR, pseudo-response regulator; RORα, retinoic acid receptor (RAR)-related orphan receptors; TIM, timeless; TOC1, timing of cab expression 1; VVD, vivid; WC, white collar; WCC, white collar complex. Modified from Saini R. et al. (2019) No special permission required.

TABLE 1.

It is believed that circadian clocks appeared very early in evolution as an adaptive function linked to DNA replication. By limiting DNA replication to the night phase, UV-induced damage to DNA could be blocked ( Pegoraro and Tauber, 2011). Over geological time selective pressure turned this simple passive process into an active one, allowing anticipation of predictable changes. Among the myriad daily and annual functions displaying clock-controlled rhythmicity are the rest/activity cycle, food intake, flowering, vertical and horizontal migration, growth, reproduction, and many more ( Table 1). In addition to their ubiquitous character and the persistence of rhythmic activity under constant light (LL) or darkness (DD) (free-running), other characteristics of a circadian clock include (1) genetic determination ( i.e., each species has its proper period close to 24 h, but inter-individual variations are observable within the same species), (2) synchronization by other factors ( e.g., rainfalls, moon cycles, food intake, tides) in addition to the LD cycle; (3) temperature compensation, i.e., the clock's period is not affected by temperature; (4) lengthening or shortening of the period with light intensity under constant light (LL); (5) induction of phase advances or phase delays by light sequences applied at different times under DD; (6) resynchronization by an environmental stimulus once constant conditions have ended. Virtually all cells possess internal clock machinery.

It is worth mentioning that in addition to the circadian clocks many organisms have developed circannual time measuring systems. As is the case for the circadian clocks, circannual clocks are ancestral, ubiquitous, autonomous, entrained by photoperiod and temperature compensated ( Lincoln, 2019). The location and mechanisms of the circannual clocks, still poorly understood, are discussed elsewhere ( Numata et al., 2015; West and Wood, 2018; Wood and Loudon, 2018; Murphy, 2019).

Localization of the Circadian System

Plants

There is evidence that multiple and distinct circadian clocks are present in different tissues of plants. The first example was obtained from bean plants, in which stomatal opening, photosynthesis, and leaflet movement rhythms displayed different periods under free-running conditions. In addition, it seems that in some cells the 24 h LD cycle is the dominant synchronizing factor, while in others it is the 24 h temperature cycle. The question has arisen as to whether there is a central pacemaker or a hierarchical coupling between different clocks in plants as is the case in animals, and how these different clock activities synchronize with each other. It has been hypothesized that the oscillations in sugar concentrations and/or microRNA (miRNA) might play this role ( Endo, 2016).

More is known in invertebrates and vertebrates, where all cells possess molecular clock machinery, forming a network of more or less potent and hierarchically organized units ( Falcón et al., 2007b; Dibner et al., 2010; Vatine et al., 2011; Ito and Tomioka, 2016). The hierarchical order varies according to the class and species considered.

Vertebrates

In fish and lizards, the circadian system is made of a network of independent and interconnected light-sensitive oscillatory units located in the retina, the pineal gland and probably also in the brain ( Tosini et al., 2001; Falcón et al., 2007b). Studies in the zebrafish indicated that virtually all cells from any tissue are light sensitive circadian oscillators ( Steindal and Whitmore, 2019), but the great variety of fish species precludes making any generalization. In any case, the pineal gland appears to act as a potent master oscillator, depending on the species ( Underwood, 1989; Whitmore et al., 1998; Figure 11). The photoreceptor cells in the retina and pineal gland actually constitute full circadian systems by themselves, as they possess the light transduction machinery that provides input to the clock, as well as the machinery that produces the output signal of this clock, i.e., melatonin ( Pickard and Tang, 1994; Bolliet et al., 1997; Gothilf et al., 1999). A major difference between the retina and pineal gland lies in the fact that retinal melatonin is generally used and metabolized locally ( Figure 11). In the pineal gland, melatonin is typically produced in higher amounts at night than during the day, and is immediately released into the blood or cerebrospinal fluid. The duration of this nocturnal signal reflects the duration of the night, while its amplitude varies with temperature in a species-specific manner ( Underwood, 1989; Falcón, 1999). Thus, daily and annual variations in the melatonin secretion profile provide a reliable indication of daily and calendar time, which is used as a time-keeping signal to synchronize physiological and behavioural processes with daily and annual variations in photoperiod and temperature (see section "Clock Outputs and Photoperiodism").

The strength and reliability of the melatonin time-keeping signal is reflected in its conservation throughout vertebrate evolution. However the modality of melatonin production has been profoundly modified from fish to mammals as a result of dramatic structural and functional modifications of the whole circadian network. In mammals, the circadian components are located in distinct specialized areas. A "master clock" is located in the suprachiasmatic nuclei (SCN; ∼5,000 to 30,000 cells) of the hypothalamus, which interacts with a network of peripheral oscillators ( Harder and Oster, 2020). Photoperiodic input to the SCN comes from the retina via the retino-hypothalamic tract: while light information encoded by the retina is mostly directed to the visual cortex through ganglion cells (RGC), a small number of these - the melanopsin-containing or intrinsically photosensitive (ip) RGC (see section "Type II or Animal Rhodopsins") - send information to the SCN (as well as numerous other brain nuclei) ( Do, 2019). One downstream effector of the SCN is the pineal gland, with its rhythmic melatonin production; but the gland has lost all intrinsic photoreceptive and circadian properties ( Collin et al., 1988; Klein et al., 1997). Rhythmic information from the SCN is transmitted to the pineal gland via a poly-synaptic neural pathway ( Klein et al., 1997; Falcón et al., 2007b). The few studies performed in Sauropsida (birds and reptiles) indicate that melatonin secretion by the pineal gland is controlled by both direct and indirect photosensitivity ( Cassone, 2014).

Invertebrates

Insects include more than 1 million species, displaying a huge diversity in all aspects of organization and life style, and there is much variation in the anatomical organization of the circadian network in the insect brain ( Bloch et al., 2013). Despite this diversity, there are striking similarities in the principal organization of circadian clocks. In the fruit fly Drosophila melanogaster the network consists of a few hundred neurons ( Hermann-Luibl and Helfrich-Foerster, 2015). A master clock is located in scattered nuclei located in the optic lobes and brain, composing a neuronal network ( Tomioka and Matsumoto, 2010; Hermann et al., 2013; Hermann-Luibl and Helfrich-Foerster, 2015). These neurons utilize mainly neuropeptides as signalling molecules, including pigment-dispersing factor (PDF), which appears to be well-conserved in putative master clock neurons of all insects studied so far (including apterygotes, orthopteroids, coleoptera, hymenoptera, lepidoptera and diptera Tomioka and Matsumoto, 2010). In D. melanogaster, PDF is considered as the main output factor of clocks, acting as a neuromodulator and synchronizing signal between the different central clock neuron clusters ( Helfrich-Forster et al., 2011; Hermann et al., 2013). In addition to these central clocks, there is evidence indicating that many other organs or tissues, either nervous (eye and eye stalk, antenna) or peripheral (gustatory system, Malpighian tubules, prothoracic gland, epidermis secreting endocuticle, testis and germinal vesicle), express circadian clock properties ( Tomioka et al., 2012). Photoperiodic information captured by the ocular, and in some instances the ocelli photoreceptors, entrains the central oscillators, which in turn deliver information to slave peripheral oscillators. In crickets and cockroaches this pathway is essential ( Tomioka and Matsumoto, 2010; Tomioka et al., 2012). In other species ( e.g., Drosophila) the central brain and some of the peripheral oscillators are fully integrated circadian systems as they are able to capture light and thus synchronize their clocks and output functions in vitro ( Tomioka et al., 2012), in a manner similar to that described for the zebrafish ( Whitmore et al., 1998). In the eye, the Rh1 and Rh6 rhodopsins are implicated in entrainment to red light ( D. melanogaster), while in the brain and peripheral oscillators it is likely to be the UV A/blue pigment Cry1 (drosophila D. melanogaster and Monarch butterfly Danaus plexippus) (see section "Phytochromes") ( Tomioka and Matsumoto, 2010). It is noteworthy that the central brain circadian system is highly plastic as photoperiodic changes have been reported in fibre distribution or number of clock neurons ( Shiga, 2013).

The Molecular Mechanisms of Circadian Clocks

The purpose here is to highlight the universality of the underlying principle as well as the wide range of situations encountered regarding the qualitative aspects of clock entrainment by light ( Bhadra et al., 2017; Saini R. et al., 2019).

Irrespective of the organism studied, the molecular clock mechanism consists of one or more transcription/translation negative feedback loops of varying complexity ( Figure 10). Because the functioning of the clock involves similar operating mechanisms with different molecular actors, it is thought that clocks have appeared independently several times during evolution ( Pegoraro and Tauber, 2011). The number of these actors varies from a few (fungi, green algae) to many (plants, animals) ( Saini R. et al., 2019). The molecular mechanisms of the circadian clocks, have been described in detail in Cyanobacteria, fungi ( Neurospora crassa), plants ( Arabidopsis thalliana), green algae ( Chlamydomonas reinhardtii, Ostreococcus tauri), insects ( Drosophila melanogaster) and several representatives of vertebrates including human ( Tomioka and Matsumoto, 2010, 2015; Ukai and Ueda, 2010; Nakamichi, 2011; Peschel and Helfrich-Forster, 2011; Vatine et al., 2011; Hurley et al., 2015; Ito and Tomioka, 2016; Koritala and Lee, 2017; Gil and Park, 2019). Strong conservation of the operating modes is observed between insects and mammals, including at the level of the molecular actors ( Tomioka and Matsumoto, 2015; Figure 10). It is worth mentioning that post-transcriptional regulation and protein modification, such as phosphorylation and oxidation, have been hypothesized as alternatives ways to building a ticking clock ( Millius et al., 2019).

Light Input to the Clock

Light is the main input to the clocks. The effects on the circadian timing systems depend on the intensity, duration, spectrum and pattern of the light stimulus; for a review in humans see Prayag et al. (2019). In the animals investigated thus far, short and middle wavelengths are strongly involved in synchronization and entrainment. In vertebrates, the effective wavelengths are comprised between 420 and 500 nm, the highest efficiency being obtained between 450 and 480 nm ( Ramos et al., 2014; Prayag et al., 2019). In mammals, this corresponds to the spectral response of melanopsin from the ipRGC of the retina (see " Type II or animal rhodopsins"). However, it is not excluded that the mechanisms of light-induced clock entrainment are more complex than believed. Indeed, it has been observed that colour opponent mechanisms can induce phase advances or phase delays in the circadian rhythm, depending on light intensity and spectral composition, in the pineal organ of fish, frogs and lizards ( Spitschan et al., 2017). Opposing effects of wavelengths on circadian phase shifts have been shown in the cave-dwelling bat Hipposideros speoris (blue vs. green) and wild rabbit Oryctolagus cuniculus (blue vs. yellow). It is noteworthy that a subset of ipRGC, sensitive to UV is also indirectly sensitive ( via cone perception) to yellow wavelengths in the mouse Mus musculus.

In insects such as D. melanogaster and other flies, Cry1 is involved both in light capture (see section "Cryptochromes") and molecular function of the clock ( Figure 10; Saunders, 2012). Cry1 is sensitive to blue light (λmax 470). In addition, Rh1 and Rh6 are implicated in entrainment to red light, and Rh1, Rh5, and Rh6 to green and yellow light ( Tomioka and Matsumoto, 2010).

In plants, a variety of situations is observed regarding the wavelengths that entrain the clocks. In terrestrial higher plants, e.g., A. thaliana, phytochromes (see section "Phytochromes") mediate the effects of red and infrared wavelengths (λ: 700-750 nm), while Cry1 and Cry2 mediate the effects of blue light ( Figure 10; Chen et al., 2004; McClung, 2006). In microalgae such as C. reinhardtii the clock is reset by a wide range of wavelengths: violet, blue/green and red ( Niwa et al., 2013; Ryo et al., 2016). Finally, in fungi the light entrainment of the clock is mediated by the WC1 blue photoreceptor species ( Bhadra et al., 2017).

Clock Outputs and Photoperiodism

Clocks control a wide range of peripheral oscillators and related downstream processes, many of them vital, to keep in phase the myriad rhythmic events that take place over the course of a day or a year. We present below a short overview (summarized in Table 1), with the help of a few examples taken from unicellular organisms, fungi, plants and animals.

Unicellular Algae, Plants, and Fungi

Neurospora crassa was the first fungi in which endogenous circadian control of its sexual and asexual daily rhythms of reproduction was demonstrated ( Zámborszky et al., 2014; Hurley et al., 2015). The asexual cycle consists in the production of conidia during the subjective night, and similar rhythms in conidiospore formation have now been reported in Myxomycetes, Zygomycetes and Ascomycetes ( Correa and Bell-Pedersen, 2002). In N. crassa and other multinucleated fungi ( Physarum polycephalum and Aspergillus nidulansone), LD cycles also synchronize the timing of mitotic cycles ( Edmunds, 1988; Hong et al., 2014). The involvement of the circadian clock has been demonstrated in Neurospora, in which 15-20% of the genes are clock-controlled ( Zámborszky et al., 2014) ( Table 1).

Virtually all functions of unicellular algae are rhythmic and synchronized by the LD cycle, including metabolism, enzymatic activities, photosynthesis, cell division cycle, mobility, morphology and chromosome topology, and even the susceptibility to drug treatments or infection by viruses ( Table 1; Edmunds, 1984). The outputs are generated by 24 h LD rhythms in gene transcription/translation ( Welkie et al., 2019).

Similarly, in more distantly related plants such as A. thaliana, the rhythms controlled by the circadian clock are plethoric, including gene expression, Ca ²⁺ fluxes, chloroplast movements, stomata opening, flowering, cotyledon and leaf movements, metabolic and hormonal activities, or defence against pathogens ( Barak et al., 2000; Table 1). In a large scale study comparing nine representatives of Archaeplastida, including unicellular algae ( Cyanophora paradoxa, Porphyridium purpureum, Chlamidomonas Reinhardtii), pluricellular algae ( Klebsormidium nitens), mosses ( Physcomitrella patens), early vascular plants ( Selaginella moellendorffii), and late vascular plants ( Picea abies, Oryza sativa, A. thaliana), it was found that they had similar diurnal transcriptional programs, despite large phylogenetic distances and dramatic differences in morphology and lifestyle ( Ferrari et al., 2019; Table 1).

Animals

Impact of Alan and LEDs on Living Organisms

" Nature is perfect. I keep a diary. I write on which day of the month the flowers bloom and on which day of the month the insects begin to sing. Year after year, these dates hardly vary. They are very regular, this is one of the laws of nature. What goes with the laws is nature. Nature is in accordance with the laws. That's why I believe people should live by imitating nature... Nature does the truth in silence."

Master Ekiyo Miyazaki (1902 - 2008).

The Generalization of LED Illumination

Initially motivated by the desire to provide more energy-efficient light sources for public lighting ( Nair and Dhoble, 2015), the use of LED now concerns a wide range of technological, socio-economic and commercial applications. A variety of sources contributes directly or indirectly (glowing) to outdoors LED lighting: offices and homes, street lighting ( Figure 1), vehicles, traffic signs, commercial advertising, tourism (architectural and landscaping enhancement), industry (factories, greenhouses), or recreational (outdoor and indoor sports) areas. Aquatic environments are also affected (shorelines and coastlines in urban and suburban areas, offshore platforms, commercial routes or fishing areas, especially night fishing). From such considerations it can be argued that investigations on the effects of outdoors LED are closely associated to those of ALAN, a situation clearly unfavourable to the preservation of the night sky.

Artificial lighting in general, and LEDs in particular, add to the list of numerous anthropogenic pressures that, decade after decade, are changing an equilibrium that has resulted from millions of years of evolution, affecting the tree of life, of which man is only one branch among thousands of others. In the vast majority of cases, studies investigating the impacts of a given factor consider mainly the effects on human health, while impacts on the animal and plant kingdoms are considered mainly within the context of improving productivity in order to satisfy growing human needs of livestock and derived products. This egocentric view is currently directing most of the research on LED; furthermore, the majority of studies are conducted in a controlled environment, while the impact on non-domesticated species and ecosystems are rarely taken into account.

We have given above an overview of the incredibly wide range of strategies that have been developed by unicellular and multicellular organisms (i) to capture and transduce light information into messages conveyed to appropriate targets, (ii) to orientate in space and time and ultimately (iii) to accomplish their essential biological needs. The development of internal clocks reflects adaptation to the highly predictable and reliable variations of the photic environment allowing anticipation and harmonization of the myriad of biological functions to the daily and annual changes of photoperiod. It is therefore not surprising that disturbances of this photic environment, whether in quality, quantity or duration, have more or less marked impacts on living organisms. Below we review, through a few representative examples, how human activities and ALAN, alone or in combination with other anthropogenic factors, alter individuals, species and communities.

Economical Purposes

Cultivation of Microorganisms and Plants

Many studies highlight the interest of LEDs for the greenhouse cultivation of plants ( Yeh et al., 2014; Nair and Dhoble, 2015; Singh et al., 2015; Dueck et al., 2016; Urrestarazu et al., 2016; Rehman et al., 2017), fungi ( Wu et al., 2013; Kim et al., 2014), and unicellular microalgae ( Schulze et al., 2014) of agronomic, ornamental or medicinal interest. One major focus resides in the possibility to choose a particular wavelength (of narrow spectral range) or a combination of wavelengths, targeting specific aspects of plant physiology in greenhouse environments ( Rehman et al., 2017). In plants, day length, light intensity, and light quality affect morphology, growth and development. The effects of light (whether by LED or other sources) on fungi and plants depend on the range of frequencies they detect. Table 2 summarizes the effects of different frequencies on the metabolism and physiology of plants. For example, far blue and UV lights are useful for eliminating bacterial and viral infections ( Yeh et al., 2014; Kumar and Engle, 2016; Kim et al., 2017), while an adequate combination of blue and red/infrared wavelengths provides optimal effects in terms of metabolism ( e.g., photosynthesis, lipid synthesis, energy production), germination, cell division, budding, growth, flowering, nutritional value and taste, or production of compounds with high added value (ergosterol, carotene). Little information is available on the impact of green lights.

However, several factors need careful attention:

(1)
The effects of a wavelength or cocktail of wavelengths depend on the species and, within the same species, on sex and stage of development; they also depend on intensity, positioning, periodicity or frequency of exposure ( Dueck et al., 2016; Hernandez and Kubota, 2016). For example, cyanobacteria grow preferentially under green, yellow and red light, whereas microalgae preferentially grow under blue (420 < λ < 470 nm) or red (λ = 660 nm) light.

(2)
Potentially toxic compounds might be produced. For example, studies on Lamb's Lettuce ( Valerianella locusta) indicate the plants can accumulate beneficial (polyphenols) as well as unwanted (nitrates) compounds depending on the proportions of red and blue light used ( Dlugosz-Grochowska et al., 2016; Wojciechowska et al., 2016). In contrast, in Brassica alboglabra nitrate concentration in shoots increased significantly when grown in the shade compared to lit areas, while it was reduced after red- and blue-LED lighting ( He et al., 2019).

(3)
The importance of plant and microbiome interactions, rarely taken into account, need more careful investigation, as light can affect both plant physiology and surrounding microbiome density and composition (including pathogenic species) differently ( Alsanius et al., 2019).

Thus, while the use of LED in the food industry is promising, it is still at an experimental stage, and studies must be conducted on a case-by-case basis, as the physiological processes involved in the responses to light are incompletely understood ( Delabbio, 2015) " For practice, more research is needed to optimize plant distances, light strategies and light intensities to make the technology more profitable and sustainable" ( Nair and Dhoble, 2015; Moerkens et al., 2016).

Breeding

As mentioned above, the quality (λ), quantity (intensity), and duration (photoperiod) of the light phase play a major role in the regulation of metabolism, physiology and behaviour in the animal kingdom ( Maisse and Breton, 1996; Malpaux et al., 1996; Falcón et al., 2007b, 2010; Rocha et al., 2013; Espigares et al., 2017). During decades, manipulation of the surrounding light conditions has been part of the protocols used to control food intake, larval development, growth rate and reproduction in farm animals ( Delabbio, 2015). For a given lighting condition, the response is species-specific; differences may also exist within the same species as a function of age, sex, or geographical location ( Pan et al., 2015).

The use of LEDs to substitute for "conventional" lighting in aquaculture farms, poultry and mammal housing is the subject of an intensive promotional campaign, which emphasizes the advantages provided by LEDs (controlled choice of wavelength and lower running costs) ( Delabbio, 2015). Field applications are still scarce ( Pan et al., 2015; Yang et al., 2016). Studies aim to compare the effects of LEDs to conventional lighting on growth, food intake and conversion efficiency, weight gain, egg production or behaviour (aggressiveness, exploration) ( Huber-Eicher et al., 2013; Pan et al., 2015). In spite of a noticeable increase in the number of publications, the data remain too scarce for definitive conclusions to be drawn. Some examples are reported below.

Impact on Species in Their Environment

Microorganisms and Plants

Artificial nocturnal illumination with white LED can influence biomass and community composition of terrestrial photoautotrophs1. In diatoms and sedimentary Cyanobacteria white LED (6300 K) induce quantitative population remodelling, loss of annual variations in population composition, decreased respiratory activity and redistribution of sedimentary microbial populations; these modifications are likely to change the CO ₂ cycle and induce carbon accumulation in sediments ( Hölker et al., 2010). Similarly, in freshwater ecosystems, three weeks of exposure to ALAN (white LED, 20 lx) decreased periphyton (the mixture of algae, microbes, cyanobacteria and detritus) biomass and the proportion of Cyanobacteria, while increasing the proportion of Diatoms ( Grubisic et al., 2017, 2018a, b). In addition, it was shown that the replacement of high-pressure sodium (HPS) lamps by white LED at intensities commonly found in urban waters (∼20 lx), induced similar but stronger effects ( Grubisic et al., 2018b). Autotrophs within periphyton communities form the base of aquatic food webs and as such constitute a fundamental element in aquatic ecosystems. More studies are needed that should include the marine environment in which ALAN disturbs synchronized diel vertical migrations of zooplankton and where the vast majority of the zooplankton pelagic community exhibits a strong light-escape response in the presence of artificial light ( Ludvigsen et al., 2018).

In plants, the intensity of lighting used in urban and suburban districts as well as on highways is sufficient to affect their physiology ( Bennie et al., 2016; Massetti, 2018). The described effects of night lighting (including by LEDs) include tree leaf colouring, retention/abscission (on deciduous trees), budding, flowering, growth, or defence against pathogens. In the case of fungi involved in litter decomposition of streams, and which play a key role in the carbon and nutrient dynamics of stream ecosystems, ALAN can alter community structure and composition, resulting in inhibition of litter decomposition ( Liu et al., 2020).

Animals

There is no longer any doubt that ALAN affects phototaxis and circadian rhythms, and consequently any ensuing functions and behaviours. It is beyond the scope of the present review to discuss the impacts of ALAN on human health and related studies ( Attia et al., 2019). Rather, we focus on the available data that can aid understanding its impacts in the wild.

FIGURE 12.

( A) Observed abundances in fish populations from the harbour of Sydney (Australia) under a 12L/12D cycle plotted in 15 min bins. Under the natural LD cycle the number of fish is higher during night (black line) than during day (blue line); they were sedentary at night with low predation activity ( P↓), while displaying a predatory behaviour during day ( P↑). ALAN (40-50 lx, warm LED light), transformed the nocturnal pattern into a diurnal one. Modified and adapted from Bolton et al. (2017). ( B) Orientation response of 4 species of sea turtles hatchlings to coloured light sources. Olive Ridley Sea Turtle Lepidochelys olivacea, Green Sea Turtle Chelonia mydas, Hawksbill Sea Turtle Eretmochelys imbricata, were attracted when illuminated with UV-A to yellow wavelengths. The Loggerhead Sea Turtle Caretta differed in that UV-A to green lights were attractive, but yellow wavelengths were repulsive, an effect reversed by red illumination. For details see ( Witherington and Martin, 2003) from which the figure was modified and adapted.

LEDs and Ecosystems

While experiments studying the impacts of ALAN on living organisms are on the increase, two aspects that need greater consideration have been only poorly investigated. One aspect is the impact on whole ecosystems, both aquatic and terrestrial. Indeed, species are linked by trophic or symbiotic interactions, and any type of impact of any anthropogenic pressure on one component of an ecosystem has consequences on the whole community, which may lead to remodelling or collapse of the entire system ( Bennie et al., 2015a, b, 2016; Sanders et al., 2015; Zapata et al., 2019). Ascending and descending effects may be observed, depending on the trophic position of the species affected. Non-trophic interactions refer to the ALAN-induced impact on pollinating or seed dispersal species (more than 75% of global crops depend to varying degrees on animal pollination), or resource competition between species with diurnal, nocturnal or twilight activity and whose activity rhythms are altered by ALAN-induced photoperiod changes. The other aspect is the impact of concomitant or successive actions of a long list of anthropogenic factors, including physical (ALAN, noise, plastics...) and chemical (pesticides, herbicides, heavy metals, nanoparticles...) pollution, climate change (rise in temperatures, oceanic acidification, changing currents...), modification and reduction of natural spaces (urbanization, deforestation, and physical barriers), etc. Together they are likely to have more than additive effects, with severe implications on species and assemblages. These issues are discussed below.

Aquatic Ecosystems: Grazing Fish and Sessile Invertebrates

Assessment of ALAN in coastal ecosystems, including estuaries, is limited ( Zapata et al., 2019), although 60% of the world's largest cities are located within 100 km of the coast, and more than 20% of coastal areas are exposed to ALAN ( Bolton et al., 2017). A study conducted in Sydney Harbour (Australia) investigated the effects of ALAN using warm light LED spotlights that provided similar or lower levels of ALAN as recorded in other urban coastal cities. Under a natural LD cycle, fish abundance, all species combined, varied over the 24-h cycle ( Figure 12A): overall, fish were more abundant, but more sedentary at night than during daytime, and predation on sessile invertebrates was higher during daytime ( Bolton et al., 2017). ALAN modified this pattern with night predation increasing to levels observed during the day. Although the abundance of fish (including predators) was markedly reduced, predation on sessile invertebrates was increased. As a consequence, the structure of the sessile assemblage was disrupted at night, which may have dramatic consequences: these assemblages perform essential activities (spawning, settlement, and feeding) at night when predation pressure is low. The authors concluded that ALAN had implications for the structure of the trophic web system that might lead to altered functioning ( Bolton et al., 2017). These data agree with investigations showing cool white LED lighting (19 lx or 30 lx at water surface) affected colonization by sessile and mobile benthic species (13 quantified), inducing reduction or suppression in some species while leading to increases in others ( Davies, 2014). Imbalance of interspecific interactions were also shown from a study on Dog Whelks Nucella lapillus. N. lapillus are widely distributed across the North Atlantic (including illuminated coastal areas) and feed on barnacles and mussels; they were more likely to, respond to, and handle prey under, a white LED light (∼21 lx) compared to controls, irrespective of the presence of a snail predator (the common shore crab Carcinus maenas) ( Underwood et al., 2017). Alterations of trophic interactions were also reported to occur under ALAN in studies performed along the Italian coast, where the population of grazing snails Melarhaphe neritoides has positive effects on the diversity of epilithic heterotrophic bacteria under a natural LD cycle ( Maggi et al., 2020). ALAN (white LED, 27 lx) modified this by reducing the density of grazers (thus erasing the positive effects on heterotrophic bacteria) and increasing autotrophic Cyanobacteria. The authors concluded ALAN was likely to alter natural systems by annihilating positive interactions across trophic levels.

Aquatic Ecosystems: Crossing Boundaries With Riparian Ecosystems

Artificial light at night, irrespective of the light source, induces redistribution of insect populations ( Meyer and Sullivan, 2013; Davies et al., 2017), some species increase in number while others decrease. Globally, observations indicate significant alterations in the number of represented species and in the size and weight of individuals. For example, mimicking street lighting levels using wide spectrum LEDs at a few sites of the Ohio river (United States), resulted in a 44% decrease in the number of tetragnathidae spiders, a 16% decrease in biodiversity and a 76% decrease in the average body size of the species; conversely, the size of neighbouring terrestrial arthropods was increased by 309% ( Meyer and Sullivan, 2013). The authors concluded ALAN altered the structure of communities in this system via changes in reciprocal aquatic-terrestrial fluxes of invertebrates. Another field study was conducted in the same area, studying the impact of ALAN (0 to 20 lx) provided by HPS and cool white LED lamps ( Sullivan et al., 2019). At moderate to high levels of ALAN, the density of predatory orb-web spiders ( Tetragnathidae and Araneidae) was particularly affected in riparian areas. At the community level, both density and family richness were affected, altering arthropod community structure; increasing ALAN induced larger proportions of predators wolf spiders, [ Lycosidae]); rove beetles ( Staphylinidae) and detritivores ( Oniscidae), and smaller numbers of omnivores (ants [ Formicidae]). In wetland systems, aquatic insect density increased and the composition of emergent insect families was different under LED or HPS or natural night lighting. ALAN also decreased the invertebrate food chain length and altered the flows of energy between aquatic and terrestrial systems ( Sullivan et al., 2019).

Terrestrial Ecosystems: Redistribution of Insect Populations

Attraction by light and redistribution of populations characterize the effects of ALAN on insects. Attraction of flying insects is a well-known phenomenon. At Hawkes Bay (New Zealand) the number of flying insects captured under street lighting sources was 48% higher when using white LED (2700 to 6500 K) than with HPS lamps ( Pawson and Bader, 2014). The authors suggested that the replacement of sodium lamps by LEDs is likely to increase the deleterious effects of ALAN with unpredictable consequences, as harmful species ( e.g., the patchy Bombyx Lymantria dispar whose caterpillars attack forests) might develop at the expense of endemic species. Also, most moths attracted by street lamps abandon fields and open ground, leading to population decreases of 50%, while biodiversity is also reduced by ∼25% ( Macgregor et al., 2015, 2017). Redistribution of surface terrestrial insect communities has been observed near light sources, regardless of the time of day or night ( Davies et al., 2012, 2017; Bennie et al., 2015a). In a 3-year experiment, it was shown that nocturnal lighting by LEDs of different quality and intensity altered the distribution of arachnid and coleopteran species on the ground ( Davies et al., 2017; Figure 13A). The effects were diminished, but not suppressed, upon reduction of intensity or duration of the light signal. Species of predators and scavengers were most represented near lighted areas, suggesting an alteration of the local ecosystem.

FIGURE 13.

(A) The impact of alternative LED lighting strategies on the total numbers of individual grassland spiders ( Araneae) (a) and beetles ( Coleoptera) (b) caught in each year, respectively. LED lighting was equivalent to that experienced at ground level under LED street lighting for HIW (high-intensity white 29.6 ± 1.2 lx), under dimmed street lighting for DW (dimmed white, 14.6 ± 0.3 lx), or under timed dimmed street lighting for DWT (14.4 ± 0.8 lx, switched off between 00:00 and 04:00 GMT). AMB was amber lighting (18.2 ± 1.3 lx, λmax = 588 nm). Controls (CON) experienced total darkness. Bar heights and error bars denote means 95% confidence intervals. Stars denote differences with the controls that were significant with 95% (*), 99% (**), and 99.9% or greater (***) confidence. From Davies et al. (2017). No special permission required. (B) Effects of artificial lighting on parameters of overall quantified nocturnal plant-flower visitor networks of seven dark sites (above) and seven experimentally illuminated sites (below). The rectangles represent insect species (top) and plant species (bottom), and the connecting lines represent interactions among species. Species codes for the plants and a list of insect species are given in Knop et al. (2017). The study was run in 14 sites of the Swiss Alps; illumination was using neutral white LED street lamps (4,000K) that provided 52.0 ± 4.2 lx on the ground. Adapted from Knop et al. (2017). More details in the original publication. With permission.

Street lighting also increased the activity of flying insects in the surroundings. They are thus likely to carry less pollen, with possible consequences on plant pollination. Such a phenomenon has been observed in a field study at sites that had never previously experienced ALAN and carried an identical variety of plants ( Cirsium oleraceum, Eupatorium cannabinum, Valeriana officinalis, Epilobium angustifolium, and Silene vulgaris) ( Knop et al., 2017). Half of the sites were illuminated at night using white LEDs (4000 K), the other half remained in the dark. Under these conditions ALAN reduced visits of pollinating nocturnal insects by 62%, with negative consequences on the reproduction of plants. In addition, the diurnal population of pollinating species was also negatively impacted. The result was a general reduction of plants as well as the insects that feed on them ( Figure 13B; Knop et al., 2017). Direct and indirect effects have also been observed in a field study in the Denver area (CO, United States), investigating the impact of ALAN (HPS lamps) on the relationship between the Smooth Brome Bromus inermis and larvae of the moth Apamea sordens that feeds on seed heads and leaves ( Grenis and Murphy, 2019). Plants growing under normal periodic darkness were hardier than those under street lamps, and the effects of street lighting on larvae were both direct (larvae were smaller when reared under streetlights) and indirect (plant traits led to reduced larval growth).

Terrestrial Ecosystems: Plants, Insects and Their Parasites

Sanders and colleagues investigated the impact of white LED street lighting (30 lx) in a plant-aphid-parasitoid community. The first investigation included three aphid species, Aphis fabae, Acyrthosiphon pisum and Megoura viciae; their parasites, respectively Lysiphlebus fabarum, Aphidius ervi, and A. megourae; and the aphids' food source, the broad bean Vicia faba ( Sanders et al., 2015, 2018). In the absence of anthropogenic pressure this community is very stable. ALAN reduced bean plant biomass and, most likely as a result of bottom-up effects, the abundance of two aphid species by 20% over five generations. For M. viciae the effect was reversed under autumnal conditions (ALAN promoting continuous reproduction of the species). All three parasitic species were negatively affected by ALAN, as a result of host number reduction ( Sanders et al., 2015). The second investigation (greenhouse and field experiments) tested the effects of different illuminance levels (0.1 to 100 lx) on the same mesocosm that also included barley Hordeum vulgare, as a resource for the aphid Sitobion avenae, and Praon dorsale, which attacks the three aphids S. avenae, A. pisum and M. viciae. The lowest levels of ALAN (0.1 to 5 lx; equivalent to severe sky glow) induced the strongest effects, reducing aphid densities by 45% as a result of parasite being twice more efficient in attacking aphids. The effects were reversed at higher light intensities because the parasites spent less time on their hosts ( Sanders et al., 2018). M. viciae was the main aphid species affected, while A. fabae responded with a negative effect at 10 lx and a positive effect at lower or higher intensities; S. avenae was not affected. There was a positive relationship between plant biomass and light intensity in the greenhouse experiment, while in the field only V. faba responded (and only at 20 lx illuminance level). According to the authors, while not discarding a possible bottom-up effect through increased plant biomass (providing more resources for aphids under higher light intensities), the interaction between aphids and parasites was the critical driver for the responses observed in the field experiment ( Sanders et al., 2018).

Terrestrial Ecosystems: Bats, Moths, and Pollination

The impacts on bats (as reported in "Animals") have major consequences on insect populations, especially moths ( Minnaar et al., 2015; Wakefield et al., 2015). The attraction that ALAN exerts on insects in general, and moths in particular, is one reason why their world population is steadily decreasing ( Macgregor et al., 2015, 2017). Attraction of moths by ALAN induces alterations in behaviour (flight, foraging or searching for sexual partners) and reproductive function. In addition, ALAN also disturbs the ultrasound detection system that some moths ( Geometridae, Noctuidae, or Notodontidae) use to detect bat predators ( Figure 14; Wakefield et al., 2015). A major consequence is the widespread reduction in moth populations and a redistribution of insect populations in the local environment. Remodelling of this kind is likely to have consequences for the entire ecosystem, affecting both plants (because moths are among the largest pollinators across the globe; see section "Aquatic Ecosystems: Crossing Boundaries With Riparian Ecosystems " above) ( Macgregor et al., 2015, 2017, 2019), and other predators (spiders and small vertebrates) that feed on these moths. Consequently, ALAN constitutes a short-term advantage for flying predators, while disadvantages appear in the medium- and long-term, with the risk of increased bat mortality (due to collision) and the scarcity of prey leading to negative population dynamics ( Altringham and Kerth, 2015; Azam, 2016).

FIGURE 14.

The mosaic plot illustrates the proportion of moth flight responses under four different conditions: absence or presence of bats ( Nyctalus sp.) under total darkness or white LED illumination, in the area of Bristol (United Kingdom). Moths respond to the presence of bats under unlit conditions at night by escape movements. This escape behaviour is markedly affected in the presence of white LED. Column width is proportional to sample size. From Wakefield et al. (2015). No special permission required.

The survival of some plants is also likely to be affected by decreases of fruit-eating and nectar-eating bats ( Lewanzik and Voigt, 2014). Carollia sowelli is an American tropical bat species important in seed dispersal of Piperaceae (pepper) and Solanaceae (potato, tomato, eggplant, chili pepper). Bats are repelled by light: in the presence of 4.5 lx HPS lighting their activity was reduced by 50%, fruit consumption by 20% and the hour of consumption delayed by more than 100%. Accordingly, this may have harmful consequences on plant reproduction ( Macgregor et al., 2015, 2017). The authors concluded that more studies are needed to further elucidate the impact of ALAN on bats and the plants that rely on them for seed dispersal and pollination (including plants of agricultural importance such as tea).

LEDs and Other Anthropogenic Factors: Some Examples

The continuous increase of human activities leads to permanent reorganization of spaces. The extension of urban and peri-urban areas, industrial and agricultural surfaces, communication routes (roads, railways, sea lanes), all lead to decreases in, and fragmentation of, natural habitats. With this come additional threats: obstacles (dams, pumps, and turbines), physical pollutants (light, noise, plastics and other trash), chemical pollutants (including endocrine disruptors [polychlorobiphenyls (PCBs), synthetic steroids, organochlorine pesticides, detergents, etc.], nanoparticles, heavy metals, radioactive waste...) and climate change (rising temperatures, ocean acidification ...). Thus, artificial light either during daytime or night-time, is not the only anthropogenic pressure on wildlife, and the question arises as to what is the impact of simultaneous and/or successive actions of these factors, since many of these targeting the same organs or associated and interconnected organs as is the case for the neuroendocrine system of vertebrates ( Figure 11). In more than half the cases, simultaneous action of several of these factors resulted in synergistic or cooperative effects, while in other cases the effects were additive or even antagonistic ( Mora et al., 2007; Darling and Côté, 2008; Côté et al., 2016). For example, overexploitation, temperature rise or habitat fragmentation, taken independently, all induce a decline in rotifer population; but taken together the rate of decline is increased by 50-fold ( Mora et al., 2007). The number of studies reporting on the combined effects of ALAN and other anthropogenic factors remains scarce.

Frogs and Midges

The singing behaviour of the male frog Engystomops pustulosus is intended to attract females at night. A parasite of E. pustulosus, the fly Corethrella spp., is also only attracted by the song of the male at night, as during the day they are eaten by the host. In urban areas, both noise and light affected the singing behaviour of the male; and both, noise (by acoustic interference) and light (by reducing locomotor activity) diminished the ability of the parasitic midge to locate and feed on its host ( McMahon et al., 2017). The combination of the two anthropogenic factors was dramatic as it led to total disappearance of the midges. The authors highlight the need to consider the multiplicity of urban anthropogenic factors in community impact studies.

Birds and Noise

The great tit Parus major is a diurnal species very sensitive to ALAN (see section "Birds"). Under a natural LD cycle tits display rhythmic diurnal activity patterns, which differ slightly between urban and forest birds ( Dominoni et al., 2020). Both ALAN and noise affect this pattern in opposite ways: ALAN increased the overall activity while noise had the opposite effect. Both factors together had synergistic effects on night-time activities, but the effects were antagonistic for daytime activity. Moreover a significant difference was found between urban and forest birds as the interactive effects of light and noise on daytime, night-time, dusk-time and offset of activity were seen in urban but not forest birds ( Dominoni et al., 2020).

Bats and Roads

Roads destroy, fragment and reduce surface habitat, degrading habitat by introducing physical barriers, noise, light and chemical pollution, and inducing lethal injuries through collision with traffic. The effects on avian and mammalian populations (in decline) can be seen up to several km away from the roads. Bats are particularly affected by all the above-mentioned factors in a species-dependent manner ( Altringham and Kerth, 2015). For example, populations of small and low-flying bats are more affected than those of large high-flying bats. Most importantly, the above-mentioned factors exert cumulative effects with dramatic consequences that may only appear after several generations ( Altringham and Kerth, 2015).

The Migrating Atlantic Salmon - A Case Study

Catches of Atlantic salmon, Salmo salar, from the Loire/Allier (France) basin have dropped from 30,000 at the end of the 19th century to less than 1500 nowadays ( Marchand et al., 2017), without mentioning a dramatic reduction in the size of the captured animals. This population decay is due to a chain of cascading reactions ( Figure 15): (i) natural predation; (ii) overfishing (recreational, industrial, and poaching), (iii) sporadic and continuous chemical pollution due to urban and agricultural activities (including endocrine and metabolic disruptors), (iv) physical pollution due to ALAN, which affects vision (because of the strongly illuminated bridges and buildings; see section "Fish"), rhythmic metabolism, and behaviour (locomotor activity, daily vertical migration as well as down-stream and upstream migration), noise and temperature (due to global warming as well as release of warm waters from nuclear run-off basins), (v) physical barriers (pumps, turbines [particularly from nuclear plants], dams and control of water flows) ( Figures 11, 15). These are multiple sources of nuisance affecting metabolism, physiology and behaviour ( Scholz and Mayer, 2008; Casals-Casas and Desvergne, 2011; Lambert et al., 2015; Bedrosian et al., 2016). Salmon navigating long distance rivers are likely to be more affected than others, as they will face a concomitance and/or succession of these factors along a course of at least 700 km. Laboratory investigations have provided evidence that the effects of combining LED lights with endocrine disruptors or temperature changes depend on the wavelength ( Figure 11). In the perciform Oplegnathus fasciatus, bisphenol A activated hepatic and plasma markers of oxidative and lipid stress, increased DNA degradation and cell apoptosis and decreased melatonin and circulating immunoglobulins; these effects were mitigated by green (530 nm) but not red (620 nm) LED light of 0.3 and 0.5 W/m ² ( Choi et al., 2016). Similar results were obtained in C. auratus ( Jung M. M. et al., 2016). In addition, in the latter a rise in temperature of 22 to 30°C induced (1) an increase in glucose, cortisol, T3 and T4 thyroid hormones in the blood and (2) T3 and T4 receptors in the brain, but (3) a decrease in hepatic and plasma immunoglobulins. Green LED lighting or the administration of melatonin, reversed these effects ( Jung S. J. et al., 2016). Figure 11 provides a schematic presentation of how many of these factors are likely to affect the fish neuroendocrine system.

FIGURE 15.

Migration is a crucial event in the Atlantic salmon, Salmo salar. In the Loire/Allier basin a ∼800 km downstream migration brings young smolts from their hatching area to the sea, where they feed and mature. In the journey they have to face light pollution (ALAN) when crossing cities or areas of active human activities (nuclear plants, industrial areas, harbours) as well as a series of other threats of anthropogenic origin, including physical barriers, overfishing, water temperature rise, physical (noise) and chemical ( e.g., endocrine disruptors) pollution. They must run another 800 km back when returning to the spawning grounds. Altogether this addition of threats impacts on metabolic reactions and physiological regulation, including their rhythmic components, which have put the species in danger of extinction.

Conclusion

Recent years have seen a growing global awareness of the potential negative consequences of exposure to ALAN. Over the last 20 years both the number of light-emitting sources, and the intensity of radiated light, have increased dramatically across the surface of the globe, not only within vast tracts of urbanized land but also along coastal areas and even in relatively isolated regions like deserts, mountain ranges and open ocean. A fierce debate has arisen in many countries as documented scientific evidence has begun to suggest that prolonged exposure to ALAN can have adverse effects on human health, with a substantial number of studies indicating links between ALAN and sleep loss and fatigue on the short term, and cancer, metabolic syndrome, mental health and cognitive disturbances on the long term ( Lunn et al., 2017). Much of the scientific rationale underpinning these effects concerns the disruptive effects of ALAN upon the proper synchronization of the circadian clock, a fundamental regulatory system, which exists in virtually all living organisms and originated at the beginning of evolution. The over-riding principle of circadian networks is that they align inner physiology with the natural day-night cycle, in order to optimize energy expenditure. It is hence obvious that exposure to ALAN creates a temporal disturbance leading to misalignment of physiology and metabolism with the fluctuating day-night cycle. The paramount importance of this system is now recognized in subjects as diverse as agriculture and medicine, and was recently highlighted by the attribution the 2018 Nobel Prize in Medicine and Physiology to the three pioneers in the field of chronobiology.

In vertebrates including humans, a key clock-mediated process involves altered secretion of melatonin, a neurohormone involved in the regulation of many rhythmic processes but also as promoting antioxidant protection in the brain and elsewhere. Melatonin has strong impact on the neuroendocrine system. Normally secreted only during the dark, nocturnal light exposure diminishes or even suppresses melatonin secretion, which if occurring over a long period leads to overall deprivation in melatonin, with consequent problems ( e.g., sleep) and potentially longer-term effects ( e.g., on cognition, metabolism (diabetes), fertility and heart disease). It has been argued that ALAN can be considered as a source of endocrine disruption in human, since so many hormones, pheromones and metabolites are under circadian control ( Russart and Nelson, 2018). This is strengthen by the observation that ALAN together with other external cues and disruptors often target the same neuroendocrine areas in vertebrates ( Figure 11).

While the scientific literature is beginning to report many studies showing possible detrimental side-effects of ALAN upon human health and well-being, the effects of ALAN on the natural world, both flora and fauna, has been less talked about and is less prominent in the public consciousness. The constant increase in ALAN through anthropogenic activity means that nowadays large areas of the earth's surface (even including oceans) are permanently bathed in light, obscuring the natural order of alternating periods of light and darkness. The day-night cycle, and also that of seasonal changes, is a critical aspect of the adaptive responses of living organisms to their shifting environment, and a correct " reading " of these cycles is essential to the correct timing of such processes as flowering, reproduction and foraging, among many others. Living organisms have developed a huge variety of strategies to integrate the visual information and to decode time. It is not surprising therefore that ALAN impacts natural systems at all levels of organization, from unicellular to eukaryotes, from systems physiology to community structures, from population behaviour to trophic interactions.

The mechanisms of light capture and of adaptation to the daily and annual changes in photoperiod started at the origin of life, and have become increasingly complex over billions of years of evolution. ALAN is now challenging this in a time scale of decades only. The ongoing extension of urban areas contributes to the cumulative effects of ALAN together with a range of anthropogenic pressures on wildlife and ecosystems (demography, over-exploitation of resources, physical obstacles, reduction of natural spaces, pollution, climate change, etc.). The result is a dramatic acceleration in extinction of species, followed by disorganization and collapse of ecosystems. The great majority of species is unable to overcome such additive stress factors and to develop new strategies in such a short period of time. Reversing or even slowing down this process will need a profound reconsideration of our environmental policies, which implies re-examination of our modern life style. With regard to ALAN the international political decision to replace pre-existing lighting systems with LED may further complicate the current scenario, due primarily to a wider emission spectrum and an enriched emission of short wavelength light to which circadian clocks are particularly sensitive. We propose that efforts should be made to limit night-time illumination to more essential purposes ( e.g., road safety), within more narrowly defined areas and at more restricted hours. The use of directed lighting to minimize wasted un-useful radiation and with carefully selected spectral emissions should permit human activity to continue unhindered while significantly reducing the impact on species.

" What we conserve defines what we are or pretend to be. We must establish and promote comprehensive dialogs among social scientists, ecologists, and evolutionary biologists to explore the biological and cultural roots of our interactions with nonhumans and to understand the origins of our inertia in the face of the urgency of biodiversity erosion. Addressing this major challenge for humanity may also enhance our ability to respect each other in our societies" ( Sarrazin and Lecomte, 2016).

Author Contributions

JF coordinated the work and wrote the manuscript. AT, CG, CM, DA, FB-C, FV, and DH contributed to discussions and reading of the manuscript. DH contributed to English editing. All authors contributed to the article and approved the submitted version.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling editor declared a shared affiliation with one of the authors DH at the time of review.

Acknowledgments

The authors acknowledge Samuel Carré (CSTB, Nantes, France), Olivier Enouf (Laboratoire National de Métrologie & d'Essais, Trappes, France), and Arnaud Metlaine (Université de Paris, Paris, France) for their contributions to the discussions at the ANSES.

Abbreviations

ALAN

Artificial Light at Night

ccg

clock-controlled gene

Cry

cryptochromes

D

darkness

DD

constant dark

FSH

folliculo-stimulating hormone

HPS

high pressure sodium

ipRGCs

intrinsically photosensitive retinal ganglion cells

JH

juvenile hormone

L

light

LD

alternation of light and darkness

LH

luteinizing hormone

LL

constant light

LED

light-emitting diode

LOV, light

oxygen or voltage

LPS

low-pressure sodium-vapour

LWS

long wavelength sensitive opsin

PCB

polychlorobiphenyl

PDF

pigment-dispersing factor

Rh

rhodopsin

SWS1

short wavelength sensitive opsin

THS

thyroid stimulating hormone.

Funding. This review is the result of a work performed within the framework of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES; https://www.anses.fr/en) on demand of the French Government Ministry of Ecology: "Ministère de la Transition Ecologique et Solidaire" ( https://www.ecologique-solidaire.gouv.fr/).

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Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

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The present review draws together wide-ranging studies performed over the last decades that catalogue the effects of artificial-light-at-night (ALAN) upon living species and their environment. We provide an overview of the tremendous variety of ...

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JMU -Light Pollution: The Overuse & Misuse of Artificial Light at Nigh

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JMU -Light Pollution: The Overuse & Misuse of Artificial Light at Nigh

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We simply do not see the night time sky in much of the continental USA as our predecessors saw it just 2 generations ago. To make this case, have a look at the two images in this section.

The first image below shows Harrisonburg, Staunton, Waynesboro, Charlottesville, Shenandoah National Park etc. In this image, taken from a space-based satellite in 2012, you can see the enormous light footprint of our cities and towns. You may look at an image like this and perhaps you say, "Yeah, those big-city folks in Harrisonburg, Staunton, Charlottesville really don't see any stars." Which is true, and by comparison to your sky where you live in one of those darker areas, you see many more stars than we do. BUT what an image like this fails to capture is the overall sky brightness because of poorly designed light fixtures that produce light pollution.

In the second image, you see how bright the skies are over Virginia and how this is measured. This sky brightness measurement is referred to as the "Bortle Scale" where a high number is bad. For instance, the night sky in Times Square would be a 9 -- you wouldn't see any stars from that location. By comparison, the cities of Harrisonburg, Staunton, Waynesboro, Charlottesville is a "5", meaning bright skies where you effectively see nothing but the brightest stars. More alarmingly, the skies above Shenandoah National Park, ranks as a '4'. So, yes, better than Charlottesville, better then Staunton, better then Harrisonburg, in that you do see more stars and you may even see the faint nebulosity of the Milky Way Galaxy, BUT it is nowhere near as dark (and the Milky Way as bright!) as our predecessors saw it just 2 generations ago.

As we start heading west into West Virginia, and Shenandoah Mountain and the George Washington National Forrest, we start finding sky brightness drop to about "2" on the Bortle scale ( see image below for the quality of our night sky changes as the Bortle Classification changes). This about the darkest skies you will find anywhere on the eastern seaboard now and even those dark skies are in endanger of being lost due to plans for development, fracking, etc.

One story that Paul Bogard, author of the critically-acclaimed book " The End of Night: Searching for Natural Darkness in an Age of Artificial Light", likes to relate when he began the research for his book, is that he asked the National Park Service where in the USA he would need to go to experience really dark skies, like a Bortle Class 1 sky. Their response? Australia.

Our night sky is very bright everywhere. And unless we do something, we will slowly erase all the stars from our night sky, even where you live.

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Light Pollution: The Overuse & Misuse of Artificial Light at Night

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We simply do not see the night time sky in much of the continental USA as our predecessors saw it just 2 generations ago. To make this case, have a look at the two images in this section. The first image below shows Harrisonburg, Staunton, Waynesboro, Charlottesville, Shenandoah National Park etc.

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Threats to Birds: Collisions (Buildings & Glass) | U.S. Fish & Wildlife Service

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Every year more than one billion birds collide with glass in the U.S. alone! While most fatal collisions happen at homes and buildings shorter than four stories tall, smaller structures like glass walkways and bus stop shelters also pose a threat.

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Birds and buildings - reflective glass is not good for birds

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Birds and buildings - reflective glass is not good for birds

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Threats to Birds: Collisions (Buildings & Glass) | U.S. Fish & Wildlife Service

# data[].attributes.attachment_link.description
Every year more than one billion birds collide with glass in the U.S. alone! While most fatal collisions happen at homes and buildings shorter than four stories tall, smaller structures like glass walkways and bus stop shelters also pose a threat.

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Why Do Birds Migrate at Night — Friends of the Forest

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Long-distance migration is an effort that tests both the birds’ physical and mental capabilities. The physical stress of the trip, lack of adequate food supplies along the way, bad weather, and increased exposure to predators all add to the hazards of the journey.

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UD study looks at how light pollution lures birds into urban areas during fall migration- City lights are an attraction for migrating birds

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UD study looks at how light pollution lures birds into urban areas during fall migration- City lights are an attraction for migrating birds

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City lights are an attraction for migrating birds

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UD study looks at how light pollution lures birds into urban areas during fall migration

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Bright lights, big cities, big problems for migrating birds - The Wildlife Society

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The effects of bright cities on migratory birds isn’t something to take lightly, but the biggest cities may not have the biggest impact on long-term journeys. Instead, cities that lie…

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Excellent TEDx talk City Lights, Beautiful Nights | James Lowenthal | from 2016.  

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Excellent TEDx talk City Lights, Beautiful Nights | James Lowenthal | from 2016.  

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City Lights, Beautiful Nights | James Lowenthal | TEDxSpringfield

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Inside the Rise of 7,000 Starlink Satellites – and Their Inevitable Downfall

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Elon Musk’s internet satellites have been a game changer for people in rural areas, but scientists are alarmed that plans to launch thousands more will be perilous for our skies.

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Shedding light on dark taxa: exploring a cryptic diversity of parasitoid wasps affected by artificial light at night - Scientific Reports

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Shedding light on dark taxa: exploring a cryptic diversity of parasitoid wasps affected by artificial light at night - Scientific Reports

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Abstract

Artificial light at night (ALAN) contributes to the globally observed insect decline. ALAN attracts nocturnal insects from their native ecosystems and disturbs their functions in the food web. Road lights in this context are ubiquitous and relevant ALAN sources that are often not considered in conservation approaches. In a previous study we showed that shielded LED road lights are suited to be part of conservation measures by effectively reducing the attraction of nocturnal insects. Here we show that this positive effect holds true for parasitoid wasps in an experimental BACI design (Before-After-Control-Impact). Combining morphological with molecular and phylogenetic analyses, we identified 106 individuals (62 morphotypes) of a minimum of 45 genera out of 13 Hymenoptera families. We were able to identify 21 species, 11 of which are newly reported in Southern Germany (Baden-Württemberg). Further combining knowledge on life history and host appearance from our data and the literature, we discuss potential impacts of ALAN ranging from an influence on nocturnal pollination via parasitoid pressure on moth species and biological control of invasive pest species to tritrophic interactions between primary and secondary parasitoids. We conclusively think that shielded LED road lights will reduce the ecological impact of ALAN on parasitoid wasps in a large and undescribed number of taxa with different host associations, likely affecting associated ecosystem functions such as biological control.

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Introduction

Artificial light and parasitoid wasps

Natural light-dark cycles, defined as daily, annual and lunar cycles that are stable across geological and thus evolutionary time scales, are crucial for synchronisation of many physiological and behavioural processes1,2. In this context, it is hardly surprising that artificial light at night (ALAN) has been identified as one of the causes of the worldwide insect decline3,4. This decline will likely have severe effects on energy/material flows and consequently on important ecosystem functions and services associated with insects (e.g. biological control, plant pollination, primary production, decomposition, nutrient cycling5,6,7). Among Hymenoptera, parasitoid wasps represent a hyper-diverse functional group with a wide range of undescribed species, so called "dark-taxa", and host organisms, many of them playing important beneficial roles in integrated pest management8,9,10. While the sparse research in the field of ALAN and biological control focuses on model systems and population dynamics (e.g. plant-aphid-parasitoid) which are important in many temperate terrestrial ecosystems11 and play a major role in the control of economically relevant pest species12, few studies investigate naturally occurring parasitoid communities. Further, many studies investigating direct behavioural responses of parasitoids to light are conducted under confined artificial laboratory conditions13 and lack reference to field conditions with numerous relevant factors for parasitoids that can influence their behaviour (e.g. light competition, host abundance, olfactory cues, natural variability of abiotic parameters).

The attraction effect

While in pest control (e.g. light trapping in greenhouses) attraction is often a desired effect8, the attraction of insects to ALAN constitutes a major problem in natural environments. Many artificial light sources attract insects, withdrawing them from their neighbouring habitats and ecological functions in the food web14,15. By affecting host and parasitoid species and life stages differently, this will likely have an influence on top-down control in insect food webs with unknown consequences for associated ecosystem functions16. Mitigation strategies to reduce insect attraction are therefore urgently needed. This may be especially relevant at transition zones between protected areas and human settlements, where public outdoor lighting represents a constantly present nocturnal disturbance and intervention, often not considered in conservation approaches at state-level17. While there are different parameters (e.g. timing and duration of illumination, the spectral composition of the light source, the light intensity, the geometry of the light emission), that could be integrated into conservation measures, uncertainty remains about the best strategies for ensuring road safety and good visibility from a human perspective while minimising the attraction radius for nocturnal insects18.

Experimental design

In our experimental BACI-Setup (Before-After-control-Impact), we aimed to test the effect of spatially confining light emission when converting different less shielded conventional luminaires to tailored LED luminaires. For this purpose, we monitored the attraction effect of individual luminaires on nocturnal insects with flight interception traps over a period of two years (2021-2022). This was conducted at three municipal streets (study sites) close to nature reserves in Southern Germany, representing a gradient in skyglow (ALAN scattered back in the atmosphere) and urbanisation (urban, suburban, rural). At each study site, paired control and impact sites with similar numbers of replicate subplots (luminaires) were selected (Fig. 1). With this experimental design, control sites were not experimental controls to explain environmental variability, but were chosen to be highly correlated with the impact sites, reflecting covariates to reduce unexplained temporal variation19. At the impact sites, we converted different types of road lights with less shielded emission (LED 4000 K, high pressure sodium (HPS) 2000 K) to tailored and shielded LED luminaires (LED 4000 K, 2700 K, 2000 K) after one year. The new lights constitute a novel approach to reduce insect attraction via a tailored light emission on the target area and an external shield around the LED panels, reducing unintentional spill light in adjacent areas and the visibility of luminaire heads from a distance (described in detail in Dietenberger et al. 2024 20). The tailored and shielded lights represent a highly optimised solution for local site conditions (street width, luminaire height, spacing), being in line with EU lighting norms (EN 13201).

Hypotheses

These transitions from various conventional less shielded luminaires to tailored and shielded LEDs allowed us to test two hypotheses. Compared to different conventional luminaires without optimised light distribution, H1) tailored and shielded road lights reduce the number of attracted parasitoid wasps (abundance), and H2) tailored and shielded road lights reduce the number of attracted species among parasitoid wasps (species richness). This was possible by combining morphological, molecular and phylogenetic analyses of a "dark taxa" - parasitoid wasps. To our knowledge, no other study evaluated the attraction of mostly very small-sized (in this study ranging from 0.5 mm to 17 mm in body length) parasitoid wasps to public outdoor lighting under field conditions on this level of taxonomic resolution. In a last step we investigated reported host associations of the identified parasitoid species from the literature. We combined this with species data on Lepidoptera abundances in our experimental set up (as an important host group). In this context, we preliminary assumed that H3) road lights will affect whole host-parasitoid-complexes by attracting adult life stages of both, parasitoids and related host species.

Municipal study sites. ( a) Municipal study sites in Southern Germany (federal state of Baden-Württemberg) selected from different levels of astronomical light pollution (skyglow), different grades of urbanisation and different habitats. Map shows data from a skyglow model from Falchi et al.21 and was produced with QGIS (Version 3.1.0, www.qgis.org). ( b) Municipal study sites in Baden-Württemberg and road lights equipped with insect traps. Control luminaires (blue circles) remained untransformed (= 3 Control sites). Impact luminaires (yellow circles) were converted in Winter 2021-2022 (= 3 Impact sites). Study site 1: Alter Flugplatz Karlsruhe, grassland, urban, n = 5 luminaires per control/impact site (conversion from conventional LED 4000 K to tailored LED 4000 K). Study site 2: Backofen Riedwiesen Brühl, Rhine plain, suburban, n = 5 luminaires per control/impact site (conversion from conventional HPS cylinder 2000 K to tailored LED 2700). Study site 3: Heimbachaue Betzweiler, river plain/forest, rural, n  = 4 luminaires per control/impact site (conversion from conventional bell-shaped HPS 2000 K to tailored LED 2700/2000K). Maps data: Google, © 2022 CNES / Airbus, Maxar technologies.

Results

Light treatments

In a total of 55 sampling nights over two years (10 luminaires in 17 nights at site 1, 10 luminaires in 15 nights at site 2, 8 luminaires in 23 nights at site 3), a total of 411 hymenopteran insects out of 18 families/subfamilies were caught at three sites (Supporting Information Table S1, Figure S1). Most Hymenoptera were winged individuals of the family Formicidae (62%), 1% Others, 11% Vespinae ( Vespula and Vespa) and 26% belonged to families that exhibit a parasitoid lifestyle. The latter were subject to DNA-Analysis (see section Barcoding). In 2021, we collected 26 individuals (22 parasitoid species), in 2022 we collected 80 individuals (46 parasitoid species). In addition, 88 species of Lepidoptera (potential hosts) were identified morphologically. This data is available via the DOI included at the end of this article (File 1).

Since parasitoids were mostly singletons and the overall abundance very low (106), we compared abundances per luminaire between control and impact sites (before and after) visually in a network plot (Fig. 2) and for individual sites (Supporting Information Figure S2). When modelling parasitoid abundance in a generalised linear model, we observed that the abundance ( p = 0.01*) was affected by the interaction of period (before-after) and treatment (control-impact) (the BACI effect) (Fig. 3a, Supporting Information Table S2). The estimated BACI effect (mean Control After - mean Control Before ‐ (mean Impact After ‐ mean Impact B efore) of the model was 2.45 ± 0.77.

Parasitoid abundance was similarly affected by the treatment group (combination of period and treatment = 4 treatment groups). Models showed that only the conventional luminaires at the control sites 2022 ( After) attracted significantly more parasitoids wasps ( p < 0.001 ***) (Fig. 3b, Supporting Information Table S3) compared to conventional luminaires at the control sites 2021 ( Before). In contrast, a similarly observed increase was less pronounced and not significant at the tailored and shielded luminaires at the impact sites 2022 (after) ( p = 0.682). A pairwise comparison further revealed that only the conventional control luminaires ( A fter) attracted significantly more parasitoids than all other treatment groups and that there were no further differences between the individual treatment groups. (Supporting Information Table S4).

The species richness of parasitoids was only marginally affected by the BACI interaction term ( p = 0.0503) (Fig. 4a, Supporting Information Table S5). The estimated BACI effect of the model was 1.72 ± 0.63. The treatment groups also had a significant effect on the number of parasitoid species (species richness). The statistical models showed that only conventional luminaires at the control sites 2022 (after) attracted significantly more parasitoid wasp species ( p = 0.0153 **) (Fig. 4a, Supporting Information Table S6) in 2022 compared to conventional luminaires in the year before. This increase was less pronounced and not significant at the new tailored and shielded luminaires at the impact sites in 2022 (after) ( p = 0.736). The pairwise comparison further revealed that only the conventional control luminaires ( After) attracted significantly more parasitoid species than all other treatment groups and that there were no further differences between the individual treatment groups. (Supporting Information Table S4). (Fig. 4 b, Supporting Information Table S7).

Bipartite Species-Site-Network. Left bars represent total parasitoid abundance at Control and Impact Sites before and after the conversion to tailored and shielded LEDs at the Impact Sites. Right bars show parasitoid taxa. Numbering of sp.-species refers to different morphotypes. Width of bars corresponds to abundance (white numbers). Before (2021): n = 26 samplings (Site 1: Alter Flugplatz, five luminaires per control and impact site, eight samplings; Site 2: Backofen Riedwiesen, five luminaires per control and impact site, eight samplings; Site 3: Heimbachaue, four luminaires per control and impact site, ten samplings). After (2022): n  = 29 samplings (Site 1: Alter Flugplatz, five luminaires per control and impact site, nine samplings; Site 2: Backofen Riedwiesen, five luminaires per control and impact site; seven samplings; Site 3: Heimbachaue, four luminaires per control and impact site, 13 samplings).

Results of generalised linear models on parasitoid abundance. ( a) The BACI-effect on the number of parasitoids per road light (Abundance, points) between control and impact sites (colours) before and after the intervention. Error bars show model predictions (points) and 95% Confidence intervals. ( b) Pairwise differences in the total number of parasitoids per road light (Abundance) between treatment groups (control before, control after, impact before, impact after). In each group, there were 14 luminaires. Letters refer to a Tukey post-hoc test. Different letters indicate significant differences. 2021 (Before): n = 26 samplings, (Site 1: eight samplings, Site 2: eight samplings, Site 3: ten samplings; 2022 (After): n = 29 samplings (Site 1: nine samplings, Site 2: seven samplings, Site 3: 13 samplings). Treatment groups: Control sites (before): (conventional LED 4000 K ( c), HPS 2000 K ( d, e)); Control sites (after): (conventional LED 4000 K, HPS 2000 K), Impact sites (before): (conventional LED 4000 K, HPS 2000 K); Impact sites after (tailored and shielded LED 4000 K ( f)/HPS 2700 K ( g, h) in 2022). Error bars show model predictions (points) and 95% Confidence intervals. Parasitoid drawings derived from Goulet et al. (1993).

Results of generalised linear models on parasitoid species richness. ( a) The BACI-effect on the number of parasitoid species per road lights (species richness, points) between control and impact sites (colours) before and after the intervention. Error bars show model predictions (points) and 95% Confidence intervals. ( b) Pairwise differences in the total number of parasitoid species per road light (species richness) between individual treatment groups (control before, control after, impact before, impact after). Letters refer to a Tukey post-hoc test. Different letters indicate significant differences. In each group there were 14 luminaires. 2021: n = 26 samplings (eight samplings Site 1, eight samplings Site 2, ten samplings Site 3; 2022: n  = 29 samplings (nine samplings Site 1, seven samplings Site 2, 13 samplings Site 3). Treatment groups: Control sites (before): (conventional LED 4000 K, HPS 2000 K); Control sites (after): (conventional LED 4000 K, HPS 2000 K), Impact sites (before): (conventional LED 4000 K, HPS 2000 K); Impact sites after (tailored and shielded LED 4000 K/2700K/2000K in 2022).

DNA barcoding

A total of 106 individuals, belonging to 13 families within the Hymenoptera reported to show a parasitoid lifestyle, were investigated. When comparing the morphological and COI-based phylogeny, our results show that the examined parasitoid individuals represent 62 different morphotypes of at least 45 genera out of 13 Hymenoptera families (Supporting Information Figures S3-S155, Table S8). We successfully barcoded 95 out of 106 specimens and determined the remaining individuals (11) morphologically to family and/or genus level. From 95 sequences, 24 CO1 sequences were determined to species level (Supporting Information Table S9), representing 21 different species. The remaining individuals were identified on genus (53 individuals) or family (18 individuals) level. The COI-based phylogenetic tree confirmed our identifications (Supporting information Figure S156). Due to low sequence length, we discarded 5 of 95 sequences here. Additionally, we identified 3 species with no COI reference sequence in Germany (Global Biodiversity Information Facility (GBIF)) (Supporting Information Table S10). Further, 14 of the species identified here have not been reported on a molecular basis in the federal state of Baden-Württemberg (GBIF). Of these, 11 species ( Aliolus Lepidus (Haliday 1835), Apanteles sodalis (Haliday 1834), Aphidius rhopalosiphi (De Stefani Perez 1902), Asobara rufescens (Forster 1862), Blacus ruficornis (Nees 1811), Diglyphus isaea (Walker 1838), Exallonyx nixoni (Townes 1981), Meteorus affinis (Wesmael 1835), Omphale lugens (Nees 1834), Omphale radialis (Thomson 1878), Stenomacrus affinitor (Aubert 1981) were not reported for Baden-Württemberg elsewhere in the available literature (Supporting Information Table S10). Host associations reported from the literature can be seen in Supporting Information Table S10.

Discussion

Light treatments

The analyses of this Before-After-Impact-Control experiment showed that the applied intervention (the transformation from different conventional lighting techniques to spatially optimised LED road lighting with shielding) resulted in a reduced attraction of parasitoid wasps in terms of abundance at three municipal streets close to nature reserves in Southern Germany (supporting H1). In addition, the conventional luminaires at the control and impact sites were not significantly different in terms of parasitoid attraction before the intervention, representing an important prerequesite for a proper evaluation of this simulated conversion scenario.

These results over two seasons were obtained from a broad spectrum of environmental conditions, grades of urbanisation and different conventional lighting contexts and involved different light intensities and spectra. We therefore think that the observed reduction in the attraction of parasitoid wasps, which have the potential to be used as sensitive indicator species of environmental change22, strongly supports the results of our previous study20. We showed that the new tailored and shielded LED lights have a reducing effect on the overall attraction of nocturnal flying arthropods after the intervention at the individual study sites by greatly reducing the area in which insects can get confused. The reduced attraction of parasitoid wasps in this study extends these insights and additionally points out the value of reducing spill light and visibility of luminaire heads from a distance. This will likely reduce an influence on host-parasitoid interactions and subsequently on population dynamics of parasitoids and associated ecosystem functions, such as biological control, as Sanders et al. have been shown in semi-field experiments23. Their study showed that community response to ALAN in an aphid-parasitoid complex is intensity-dependent, suggesting that additional context-dependent dimming of tailored and shielded road lights could be a further improvement.

In addition, the new tailored and shielded luminaires at the impact sites in 2022 were not significantly different from overall low parasitoid abundances attracted to conventional luminaires at control and impact sites in the year before (2021), indicating that the tailored lighting design compensated for a seasonal increase in parasitoid abundance from 2021 to 2022. The factor from control to impact sites changed from x1.2 before to x4 after the intervention.

Although parasitoid species were mostly singletons and the species richness was only marginally impacted by the "BACI-effect", a pairwise comparison of the number of species (morphotypes) between control and impact sites before and after the conversion at the impact sites gave additional insights, indicating that tailoring and shielding of luminaires also reduced the number of attracted parasitoid species compared to different conventional luminaires (supporting H2). The attraction of different species to ALAN is related to different photosensitivities, but the observed reduction in the number of species in this study is most likely related to an overall reduced parasitoid abundance at tailored and shielded LEDs24. Site 3 (rural) in the Black Forest showed the highest number of parasitoids (30 species). Of 53 parasitoids in 2022, only seven individuals (13%), representing seven different species (23%) were attracted to the new tailored luminaires at the impact site in 2022. In summary, the tailored lighting approach investigated in this study reduced distracting and misleading visual cues and the number of affected individuals and species and is therefore expected to be beneficial for ecosystem services associated with parasitoid wasps in different host associations, which may be especially relevant close to protected areas, where light pollution is often not integrated into conservation approaches. We therefore propose that a tailored light distribution of neighbouring road lights should be a part of future mitigation strategies.

Barcoding

Integrative taxonomy is becoming ever more significant in biodiversity research as scientists are increasingly tackling taxonomically challenging groups such as chironomids or parasitoid wasps25. By using such an approach, we investigated the attraction of parasitoid wasps to road lights, which has provided valuable insights into a largely undescribed diversity of species affected by ALAN in Baden-Württemberg. The comparison of a COI-based phylogeny and morphological data allowed us to identify and discuss ALAN-induced impacts of 21 different insect species, of which 11 were not previously reported in Baden-Württemberg. In the following, the potential impacts of ALAN on eight parasitoid species whose life history, host association and distribution data are available, are briefly discussed:

Lepidoptera parasitoids

Apanteles sodalis(Braconidae) is a koinobiont endoparasite of lepidopteran larvae26, emerging at Site 2 in the upper rhine plain in September 2021 at conventional HPS 2000 K luminaires. A potential lepidopteran host species is Archips rosana ( Tortricidae), a relevant pest of different soft fruits27. Potential Tortricidae hosts at conventional HPS at Site 2 were Pandemis heparana and Eucosma metzneriana emerging in mid-June 2022.

Diadegma fenestrale (Ichneumonidae) was attracted to conventional LED 4000 K in late September 2021 at Site 1 in Karlsruhe. Diadegma fenestrale is known to attack the larvae of Plutella xylostella, one of the most relevant lepidopteran pest species of brassicaceous crops and has been introduced as a biocontrol agent in several countries in Europe28,29. Plutella xylostella (microlepidoptera) has a cosmopolitan distribution and was attracted to conventional LED 4000 K at Site 1 in September 2022.

Amblyteles armatorius (Ichneumonidae) has a wide distribution across Europe (GBIF). The larvae of this species emerge from the pupae of two lepidopteran genera ( Xestia and Noctua)30. Amblyteles armatorius was attracted to road lights at Site 1 (conventional LED 4000 K) in October 2022. Likewise, four potential host species (X. c-nigrum, X. stigmata, X. xantographa and N. Pronuba) were attracted to conventional LED 4000 K at Site 1 in August in 2021, July 2022 and September 2021 and 2022 31,32.

In summary, the observed attraction effect of ALAN on adult life stages of several Lepidoptera parasitoids and hosts points to an influence of road lights on whole host-parasitoid-complexes (supporting H3). Subsequently, this suggests a large-scale influence of public outdoor lighting on parasitoid pressure on Lepidoptera populations. This could influence nocturnal pollination by moths and therefore plant reproductive success, which may cascade to the diurnal pollinator community15,23. We showed that tailored and shielded road lights effectively reduced unwanted light emission and parasitoid attraction in different real traffic and lighting scenarios, while fulfilling EU-norms. This will most likely also reduce an impact on Lepidoptera populations via parasitism under different environmental and lighting contexts and should be integrated into future lighting concepts.

Potential Spotted Wing Drosophila (SWD) Parasitoids

Pachycrepoideus vindemmiae (Pteromalidae) is an idiobiont ectoparasitic wasp attacking pupape of different cylorrhaphous flies31. It was one of the few parasitoids in total (16 of 80 in total at three sites in 2022 = 20%) that was attracted to the new tailored and shielded luminaires, in this case tailored LED 4000 K at the urban Site 1. Its potential as a biocontrol agent has been tested in several European countries, since it is one of the main parasitoids of the invasive Asian fruit fly Drosophila Suzukii Matsumara 1931 (SWD) in Europe, an economically important pest of soft fruits32,33,34. SWD was first detected in Italy and Spain in 2005 35. In Germany, SWD was first reported in 2011 in a monitoring program of the Julius-Kühn-Institute (JKI), including collection sites in the upper rhine plain36. The successful invasiveness of SWD may be related to the absence of well adapted specific antagonists in the invaded ecosystem, but knowledge on the regulative efficiency of German natural enemy communities is scarce37. This is especially investigated for the upper Rhine plain by studies from Englert & Hertz (2017)37. In the laboratory, they reared natural enemies from fruit baited traps collected at JKI Dossenheim. SWD uses a wide range of habitats and host plants (soft/stone fruits), crops as well as and ornamentals36,38. Another main parasitoid of SWD in Europe is Trichopria sp. ( cf. drosophilae) ( Diapriidae)34,37. Undetermined Diapriidae sp. (cf. Trichopria). emerged at conventional LED 4000 K at Site 1 (urban) and tailored LED 2700 K at Site 2 (suburban).

Another potential SWD parasitoid is Asobara rufescens (Braconidae). Asobara rufescens is reported from the Palearctic Region, but has been considered a junior synonym of Asobara tabida (Nees, 1834), which occurs in the Nearctic, Palearctic, Oriental, and Oceanic regions39. It appeared at conventional HPS 2000 K at Site 2 (suburban) in September 2022. The appearance of Pachycrepoideus vindemmiae, Diapriidae sp. (cf. Trichopria). and Asobara rufescens (or Asobara tabida) as potential natural enemies of SWD in this study corresponds with other European reports33,37. Interestingly, we observed another potential parasitoid of SWD, similarly originating from Asia and first reported in Europe from Italy in 2022 40 and from Germany in 2023 41, at the suburban Site 2:

Leptopilina japonica (Figitidae) was first reported in several sites in southern and western Germany in 2023, potentially reflecting a case of unintentional biological control in Germany41. Leptopilina japonica was attracted in mid-August 2022 to conventional HPS 2000 K at Site 2 (suburban). Comparing sequences with BOLD database, we found our specimen to be conspecific with a specimen (BOLD process ID: GBHYG1714-23) from the study of Martin et al. (2023). Martin et al. (2023) caught L. japonica with sweep nets in consecutive years (2021-2022) in Bonn (North Rhine-Westphalia), but also from infested raspberries in Dossenheim in 2021 (Baden-Württemberg) and conclude that adventive populations may already be established41. The appearance of L. japonica in this study at Site 2 (approximately 10 km from JKI Dossenheim) supports this conclusion. To our knowledge, it is the first molecular report of an adult individuum collected under field conditions in the upper Rhein plain (GBIF). The species could have the potential to be used in integrated pest management of invasive SWD in a natural enemy naive environment. In summary, the appearance of different SWD parasitoids across different sites in Baden-Württemberg points to a large-scale impact of public outdoor lighting on adult life stages of potential biological control agents of pest species. In any case, we showed that tailored and shielded LED luminaires significantly reduced overall parasitoid attraction, which most likely reduces an impact on host interactions of biocontrol agents. However, further ALAN field research is needed here.

Tritrophic interactions

In Europe, Sitobium avenae, Rhopalosiphium padi and Metopolophium dirhodum are among the most important aphid cereal pest species. These three aphid species are frequently attacked by a group of primary parasitoids (mostly Braconidae, Aphidiinae)42. These natural enemies can exert top-down control (biological control) on cereal aphid pest populations43, while in turn being attacked by secondary hyperparasitoids, influencing primary parasitoid mortality and consequently the levels of biological control44. For example, Aphidius rhopalosiphi is among the primary aphid parasitoids and was attracted to conventional HPS (2000 K) in June 2022 at Site 2 (suburban). Its antagonist the hyperparasitoid Alloxysta victrix (Figitidae) was attracted to conventional HPS 2000 K in June 2022 at Site 3 (rural)45. Despite the presence of the latter two species at different sites, their appearance on two consecutive nights in June 2022 (28.06.22/29.06.22) suggests a potential influence of road lights on tritrophic interactions by removing single individuals from their habitats. We showed that tailored and shielded LED luminaires reduce the attraction of parasitoid wasps, which is therefore expected to reduce an impact on tritrophic parasitoid complexes.

Material & methods

Light treatments

In a first step, nature reserves in Southern Germany were identified by categorisation into light pollution classes regarding sky brightness using night light satellite data of the "day-night band" (day and night band) of the instrument "visible infrared imaging radiometer suite" (VIIRS) on board of the Suomi-NPP satellite for recording upward directed light. For being able to make general statements on the suitability of a transition to tailored and shielded LED in aspects of insect conservation, protected areas ( n = 3) were selected from different habitat-, landscape- and light pollution contexts (Fig. 1). A site-specific monitoring and a conversion concept were developed for the locations (e.g. number of luminaires, selection of masts/luminaires, position in relation to the nature reserve, conversion options) (Supporting Information Table S11). From April to October 2021-2022, a total of 28 flight interception traps were mounted close to the luminaire heads of individual luminaires at three differentially illuminated sites (Site 1 Alter Flugplatz LED 4000 K ( n = 10), Site 2 Backofen Riedwiesen, high pressure sodium (HPS) cylinder luminaires 2000 K ( n = 10), Site 3 Heimbachaue HPS bell-shaped luminaires 2000 K ( n = 8). To ensure that the planned before-and-after comparison allows reliable statements to be made regarding the impact of light transformation on nocturnal insects, control investigations with the existing conventional lighting were carried out at all locations (Fig. 1). These control sites were as similar as possible (development, vegetation, traffic, lighting environment etc.) to the upgraded impact sites before the upgrade. Half of the trap-equipped lights at each location were converted to tailored and shielded LED luminaires between November 2021 and April 2022 (Site 1 Alter Flugplatz LED 4000 K, Site 2 Backofen Riedwiesen LED 2700 K, Heimbachaue LED 2700 K), while the other served as controls in 2022. Once on a monthly schedule, insects were sampled on consecutive nights (first night Site 1, second night Site 2, third night Site 3) close to half-moon (Supporting Information Table S11). For this purpose, containers with 80% alcohol were screwed to the bottom of the traps for the period between sunset and sunrise. During the winter season, the insect traps were dismantled and serviced to be reinstalled after the conversion. To rule out that the differences in colour temperature between conventional (HPS 2000 K) luminaires and the tailored and shielded luminaires (LED 2700 K) at Site 2 + 3 obscures the effect of an optimised light distribution, we additionally performed control experiments with the tailored and shielded luminaires and a reduced blue light content (LED, 2000 K) at Site 3. For this purpose, we attached amber foil to the exit window of the luminaire and adjusted illuminance to the same level as the control luminaires (2000 K, Em = 5.2 lx). From June to September, the tailored and shielded luminaires were modified in this way for the duration of one week after sampling with the original configuration (LED, 2700 K) and prior to five additional sampling events.

Identification

Microscopes and binoculars were used for morphological identification. Depending on taxon, animals were identified to order, family, genus, or species level46. In preparation for molecular DNA-analyses (see next section), parasitoid Hymenoptera were transferred to 99.9% alcohol and send to AIM Gmbh Leipzig. We evaluated all specimens morphologically using different taxonomic keys (Supporting Information Identification literature). To evaluate sampling efficiency and to get an estimate on the minimum number of species, the individuals were assigned to morphotypes, representing different species based on morphological criteria. In a separate taxonomic examination, Lepidoptera (constituting potential host species with partly close relationships to foraging plants) were determined to species-level by Dr. Robert Trusch and Michael Falkenberg, Naturkundemuseum Karlsruhe). Lepidoptera are stored in the Lepidoptera collection at Naturkundemuseum Karlsruhe. Subsequently, we screened available literature and online literature resources (Google Scholar, Web of Science, Global Biodiversity Information Facility (GBIF)) to gain insight into species distribution and ecology as well as reliable molecular reports from Germany and Baden-Württemberg of the identified taxa.

Barcoding

Target DNA sequences of the mitochondrial cytochrome C oxidase I (CO1) gene fragment of 106 parasitoid individuals were generated and analysed at Advanced Identification Methods (AIM GmbH, Leipzig, Germany47). Particularly, genomic DNA (gDNA) was extracted from whole individuals or parts stored in 99.9% alcohol using the Qiagen DNeasy ® Tissue Kits (Qiagen, Hilden, Germany). The gDNA was then amplified in a polymerase chain reaction (PCR) with 2 established primer combinations: LCO1490-JJ_M13f and HCO-1490-JJ_M13r 48 / dgLCO_M13f and dgHCO_M13r49). The generated PCR products were then processed on two ABI 3730 capillary sequencers with 50 cm capillary length. All raw DNA sequences were assembled and edited using Sequencher 4.10.1 (Gene Codes, Ann Arbor, MI, USA). Editing for each gene sequence was performed in MEGA v5.1 50 and searched against the Barcode of life data system v3 (BOLD) and the National Centre for Biotechnology Information (NCBI) database using the Nucleotide collection (nt/nr) database of the Basic Local Alignment Search Tool BLAST51,52. For species identification, we defined a threshold of a 97% match with the reference sequence and compared the best hit with the next three hits for consistency. All involved specimens are stored as vouchers at Leibniz-Institute for Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12784 Berlin.

Phylogenetic analysis

Complimentary, we inferred a COI phylogenetic tree using the maximum likelihood optimality criterion as implemented in the software IQ-TREE version 1.6.12 53,54 with default parameters. Particularly, for the phylogenetic data analyses all processed COI sequences were aligned using Mafft version 7 55 before running IQ-TREE. The inferred tree was rooted by selecting the two Ceraphronidae specimens as phylogenetic outgroup.

Statistics

Statistical analysis was carried out with R Studio Software Version 1.2.5033. In a first step, luminaires were assigned to site (paired control and treatment site at three study sites) (Compare Fig. 1). The control sites refer to the untransformed conventional control luminaires, the impact sites refer to luminaires that were converted in winter 2021-2022. Abundances were calculated by counting the number of parasitoid individuals per individual luminaire and year. Species richness was calculated by counting the number of species (individual morphotypes treated as species) per luminaire and year. Because we observed a general effect of the year (the 3.1-fold total parasitoid abundance in 2022 (after) compared to 2021 (before)), we proceeded modelling parasitoid abundance in a combined generalised linear model over three sites (to achieve robust sample sizes)58 in a before-after-control-impact (BACI) design19 (package "glmmTMB"56). Distribution test and model selection included "shapiro.test", "fitdistr" ("MASS" package57), "lmer", "anova" ("lmerTest" package58) and "simulateResiduals", "testDispersion", "testQuantiles","testOutliers","testZeroInflation" of the "DHARMA" package (residual diagnostics for hierarchical (multi-level/mixed) regression models59). Hypothesis testing was carried out using the "anova" function of the "stats" package60, backward selection of fixed effects and comparing AIC. We constructed GLMMs to determine how the abundance and species richness of parasitoid wasps (dependant variables) were affected by period (before-after) and treatment (control-impact) along with their interaction (the BACI effect) (fixed effects)61. We used a poisson distribution and set the zeroinflation argument to 1. We designated 2021 as "before" and 2022 as "after," and the two sites per study site as "impact" and "control" sites. We included the study site and the year as random effects. We additionally used an observation-level (luminaire) random effect. To be able to make pairwise comparison between all combinations of period and treatment, we combined these predictors into a single fixed effect (= treatment group) in models with the identical structure of random effects19,61,62. All models were checked for overdispersion, zeroinflation and autocorrelation of residuals. Post-hoc tests ("emmeans" package, method "Tukey"63) were computed to reveal the differences between individual treatment groups. Plotting was done with "ggplot"64.

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Acknowledgements

We would like to thank all involved stakeholders, municipalities and administrations who have contributed to the realisation of this project. We thank Daniel Raddatz and Juliane Körner from Regierungspräsidium Karlsruhe for input in early study design and site selection and administrative help within NaturLicht. We thank Prof. Alexandra Maria Klein and Angela Gronert for support and access to laboratory and office at the Chair of Nature Conservation and Landscape Ecology, University of Freiburg, Germany. Additionally, we want to thank Dr. Robert Trusch and Michael Falkenberg from Naturkundemuseum Karlsruhe for Lepidoptera identification.

Funding

Open Access funding enabled and organized by Projekt DEAL.

The project "NaturLicht" is part of the "Sonderprogramm zur Stärkung der biologischen Vielfalt" in the federal state of Baden-Württemberg and funded by the regional council (Regierungspräsidium) Karlsruhe. The municipal sites in Southern Germany are part of "NaturLicht". DNA-Barcoding-Services from AIM Gmbh Leipzig were funded by "Wissenschaftliche Gesellschaft Freiburg im Breisgau".

Author information

Authors and Affiliations

1. Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Müggelseedamm 310, 12587, Berlin, Germany

Manuel Dietenberger, Andreas Jechow & Franz Hölker

2. Institute of Biology, Freie Universität Berlin, Königin-Luise-Straße 1-3, 14195, Berlin, Germany

Manuel Dietenberger & Franz Hölker

3. Chair of Nature Conservation and Landscape Ecology, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Str.76, 79104, Freiburg, Germany

Manuel Dietenberger

4. Department of Engineering, Brandenburg University of Applied Sciences, Magdeburger Str. 50, 14770, Brandenburg an der Havel, Germany

Manuel Dietenberger & Andreas Jechow

5. Natural History Museum Bern, Bernastraße 15, Bern, 3005, Switzerland

Manuela Sann

Contributions

MD, AJ, and FH designed the study, MD performed the insect experiments including identification, AJ quantified the light environment. MS conducted phylogenetic analyses, MD and MS evaluated molecular and database identification, Data were analysed by MD, AJ and FH. The original drafting of the article was done by MD, AJ, MS and FH and all authors contributed to the editing of subsequent drafts.

Corresponding author

Correspondence to Manuel Dietenberger.

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The authors declare no competing interests.

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Dietenberger, M., Jechow, A., Sann, M. et al. Shedding light on dark taxa: exploring a cryptic diversity of parasitoid wasps affected by artificial light at night. Sci Rep 15, 6237 (2025). https://doi.org/10.1038/s41598-025-88111-3
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# data[].attributes.attachment_link.title
Shedding light on dark taxa: exploring a cryptic diversity of parasitoid wasps affected by artificial light at night - Scientific Reports

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Artificial light at night (ALAN) contributes to the globally observed insect decline. ALAN attracts nocturnal insects from their native ecosystems and disturbs their functions in the food web. Road lights in this context are ubiquitous and relevant ALAN sources that are often not considered in conservation approaches.

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Dark side of bright nights taking toll on forgotten invertebrates

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Dark side of bright nights taking toll on forgotten invertebrates

# data[].attributes.attachment_link.title
Dark side of bright nights taking toll on forgotten invertebrates

# data[].attributes.attachment_link.description
From bats to moths, species working the night shift are suffering as light pollution soars

# data[].attributes.headline
Lights Out: Philly Skyscrapers to Go Dark to Protect Migrating Birds

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Lights Out: Philly Skyscrapers to Go Dark to Protect Migrating Birds

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Lights Out: Philly Skyscrapers to Go Dark to Protect Migrating Birds

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Don’t be surprised if it’s extra dark outside in Philly this spring. Some of the city’s tallest buildings are going dark to protect migratory birds as they head north.

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Many birds, particularly songbirds, migrate at night, navigating by the moon and stars. Mostly flying at altitudes below 2,000 feet, and even lower on foggy and rainy nights, they often become disoriented by brightly lit windows in tall buildings. The result is horrific: more than 100 million bird deaths in North America annually, and as many as 1,000 bird deaths per major structure, reports Massachusetts Audubon. In response, Audubon and its partners have organized Lights Out campaigns, urging buildings to hit the off-switch at night for bird safety.

In 1991 Toronto became the world's first city to address urban bird collisions when it launched the Fatal Light Awareness Program (FLAP). About a decade later Chicago became the first U.S. city to follow suit. Today, as the movement has picked up significant momentum, more than 20 North American metropolitan areas-ranging from major cities like Washington, D.C., to smaller ones like Winston-Salem, North Carolina-participate in similar programs. The programs vary, but they're typically a collaboration between an Audubon chapter and local partners and involve convincing building managers and owners to join in by educating them about the benefits.

Many cities also provide online resources for bird-friendly and sustainable development. Toronto's Bird Friendly Guidelines, for example, suggest using reflection-free glass and visual markers on buildings and outline how to use lights to optimize bird safety. Participation is voluntary, and Lights Out programs usually focus on getting buildings to take part between midnight and sunrise for several months a year during spring and fall migration, when the bulk of migrating birds are passing through.

"There are multiple reasons why Lights Out programs are valuable," says Don Gorney, program manager for Lights Out Indianapolis. "It saves bird lives and also promotes energy conservation."

Lights Out programs began to get popular in the United States about a decade ago. In fall 2001 Robbie Hunsinger, a freelance oboist turned bird advocate, attended a presentation in Chicago by the director of FLAP and immediately determined that she would do something about bird collisions and buildings. In 2002 Hunsinger founded the Chicago Bird Collision Monitors to raise awareness about bird collisions and also to collect dead and injured birds off the city's streets (see " Pain in the Glass," November-December 2008).

"I was very concerned about this, so I started contacting building managers myself and explaining that, 'Hey, we're finding a lot of dead birds at your building,' " says Hunsinger. "I made friends with doormen, sweepers, and building managers. My protocol for the program was that there were no bad feelings or angry confrontations with managers because they were working with us and allowing us on their property. One by one the buildings starting turning off their lights." Hunsinger's grassroots effort was a smashing success. By 2004 every building in Chicago taller than 60 stories hit the switch for night-migrating birds.

Hunsinger points out that her activism was built on a foundation laid by then-Mayor Richard Daley, who had set the stage for Lights Out Chicago by launching it in principle a few years before Hunsinger came along. "Mayor Daley got Lights Out all written up; they just needed someone to do this on the ground," says Hunsinger, who even earned a bird-rehabilitation license in service to the cause and donated her cell phone number as the Bird Collision hotline. "It was like the perfect storm. People were just ready to help, and it was ready to go in Chicago."

Today Chicago Bird Collision Monitors has more than 100 volunteers. Seven days a week, about a dozen of them take turns walking or biking the streets at sunrise to find dead or injured birds.

Because of Chicago's location along the Mississippi Flyway and on Lake Michigan-"an unfortunate channel," Hunsinger says-volunteers still see an incredibly high number of bird casualties. On just one September morning they found 270 injured birds and 320 dead birds, mostly white-throated sparrows, brown creepers, and golden-crowned kinglets, according to Annette Prince, who now directs Chicago Bird Collision Monitors. Other common casualties include ovenbirds, Nashville warblers, yellow-bellied sapsuckers, and hermit thrushes.

Still, it's unclear what the casualty numbers really mean. "It's hard to use bird strikes to measure program success. We actually find more birds today than we did in 2004 because we have more volunteers to cover a greater area," explains Prince. "It's doesn't mean things are getting worse; it just means we have more outreach, and I think success is measured by the awareness we raise." By that standard Chicago has clearly set a model for other cities to emulate.

That doesn't mean there aren't plenty of other success stories. Take Lights Out in Minneapolis. Joanna Eckles, coordinator of Audubon Minnesota's Project BirdSafe/Lights Out, started the program after she, like Hunsinger, heard a lecture by FLAP's director. To raise architects' awareness about bird collisions, she and her team have offered lunch-hour educational talks. They've also spread the word via the newsletter of the Minnesota Building Owners and Managers Association.

Some 60 private buildings in Minneapolis have come on board during spring and fall migrations. And last May 1 the University of Minnesota began administering both required and recommended bird safety construction guidelines, alongside other construction guidelines, to any new buildings that receive state bond money-a zoo, for instance, or a stadium or park building. One required guideline is that glass on upper floors of buildings must have visual markings to deter birds.

As in Chicago, Lights Out in both Minneapolis and St. Paul depend on a cadre of volunteers who walk mapped-out routes each morning, looking for bird casualties. Warblers and sparrows are the most commonly found species.

Also as in Chicago, statistics may be misleading. "Measuring the program effect is really a challenge because there are so many factors that aren't controllable," Eckles says. "You can test it by one problem building, but I think the real measure of success is in the awareness we have raised, like the state coming to us and asking us to put bird safety information in a state construction guideline. That's huge."

East Coast cities are also involved. Lights Out New York, for example, has been active since 2005. More than 90 of the city's buildings have signed on, including such iconic properties as Rockefeller Center, the Chrysler Building, and the Time Warner Center. "I think that Lights Out is really a win-win sort of solution," says Adriana Palmer, coordinator of New York City Audubon's Project Safe Flight. "It's a clear benefit to the birds, but for the buildings, any time they are turning off lights they are also saving energy and money."

Lights Out Boston offers yet another model. Its program was founded in the fall of 2008 by Massachusetts Audubon and Mayor Thomas Menino, and today more than 45 buildings participate, turning off both internal and decorative lights. Besides benefiting the birds, the program also helps Menino pursue his goal of decreasing Boston's greenhouse gas emissions by 80 percent by 2050.

Other cities, from Paris to Santa Rosa, California (see " Dark Side of Light," Field Notes, May-June 2013) have joined in, turning off their lights at night to save energy and help birds. In Houston companies, by becoming involved in the Lights Out program, are also supporting the city's stated goal of becoming the U.S. "Energy Conservation Capital." Then there's Earth Hour, an international tradition that began in six years ago in Australia; for one hour every March, cities and residences around the world go dark to save energy. All told, 153 countries have participated.

On the other hand, the movement is growing more slowly in some cities than others. San Francisco's Lights Out program, for example, started about four years ago under the Golden Gate Audubon Society. Although many buildings participated the first year, the chapter's small staff and limited resources have prevented it from tracking bird mortality and assessing if the program is really paying off. This year the Lights Out people designed a logo -a silhouette of birds against a city sky-in hopes it will give the program a new educational push, says Ilana DeBare, Golden Gate Audubon's communications director.

Lights Out Indianapolis, inspired by the success of Lights Out Chicago, was formed in 2009 by the Amos Butler Audubon Society. Although the program has enjoyed only modest success so far-just six buildings have signed up-things are looking up. "Since 2009 to 2012, we observed 1,299 bird strikes, counted by volunteers, and we demonstrated that certain buildings are problematic," adds Gorney. "Now, with the help of the City of Indianapolis and the help of the Indianapolis Zoo, we are making big progress educating buildings on Lights Out and bird safety." Above all, The Chase Tower, at 48 stories the city's tallest building, is in compliance.

Other more creative approaches are gaining traction. For instance, Chicago is encouraging buildings to shut off lights in lobbies, especially those with interior foliage, which can attract birds. Other cities, including Minneapolis, are pushing for changes in the way buildings are built. Eckles and others would like to see architects consider bird safety the way they currently factor in such things as energy use and heat gain. "I'd like to have bird safety be a part of what we think of sustainable design," she says.

Some have a loftier goal: cross-city collaboration. "What I would like to see is connectivity between programs, because if you think about it, these birds are making a huge trek through entire flyways," says Eckles. "I would love to see us sharing strategies and solutions, getting nationwide legislation, and coordinating efforts."

From all indications, the prospects for Lights Out programs look brighter than ever. "There was just a lot of goodwill, as nobody likes to see a dead or injured bird," says Chicago's Hunsinger. "We became on a first-name basis with doormen. Patagonia even donated organic cotton T-shirts for the volunteers. This has been just a beautiful human story."

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Programs across the continent help protect birds from colliding with buildings.

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Bird collision deaths are down in Fort Worth as downtown businesses turn off building light

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Bird collision deaths are down in Fort Worth as downtown businesses turn off building light

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Bird collision deaths are down in Fort Worth as downtown businesses turn off building lights

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For fall 2024 migration, 42 deadly bird collisions were reported, down from the 110 mortalities documented last fall.

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Artificial Light Attracts Birds to Cities and Increases Mortality, Study

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Artificial Light Attracts Birds to Cities and Increases Mortality, Study

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Artificial Light Attracts Birds to Cities and Increases Mortality, Study

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Nearly 1,000 birds were killed Oct. 4–5 when they collided with an illuminated glass building in Chicago. Though mass fatalities of this magnitude are rare, light pollution poses a serious—and growing—threat to migrating birds.

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Lights Out: A Fatally Flawed Bird Conservation Program - Ornithologycenter

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Lights Out: A Fatally Flawed Bird Conservation Program - Ornithologycenter

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Lights Out: A Fatally Flawed Bird Conservation Program - Ornithologycenter

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Using lights out to protect birds from deadly collisions is fatally flawed. If one window is shutered birds will just hit lit windows in other buildings.

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Lights out: City skylines are luring migrating birds to their deaths

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Lights out: City skylines are luring migrating birds to their deaths

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Lights out: City skylines are luring migrating birds to their deaths

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Artificial light significantly influences where migrating birds choose to land, posing a critical threat to their survival, new alarming research shows.

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Study: Light pollution is luring birds to cities – and sometimes to their deaths - Warner College of Natural Resources

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Study: Light pollution is luring birds to cities – and sometimes to their deaths - Warner College of Natural Resources

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Study: Light pollution is luring birds to cities – and sometimes to their deaths - Warner College of Natural Resources

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In the largest study of its kind, scientists used weather radar data to map bird stopover density in the United States and found that artificial light is a top indicator of where birds will land.

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City of Harrisburg - Find Community, Find Home

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Mayor Williams asking City of Harrisburg residents to go “Lights Out” to help bird migration - City of Harrisburg

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FOR IMMEDIATE RELEASEContact: Matt Maisel, Director of Communications mmaisel@harrisburgpa.gov, (717) 255-7295 HARRISBURG -- As the weather gets warmer, chances are you’ll start seeing a lot more friends flying our friendly skies over the state capital. However, it’s at night, when you can’t see the thousands of birds migrating back to their northern homes, that can

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‘Lights Out’ seeks to stem bird carnage caused by city skylines

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‘Lights Out’ seeks to stem bird carnage caused by city skylines

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‘Lights Out’ seeks to stem bird carnage caused by city skylines

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During migration season, volunteers comb the pre-dawn streets of cities in search of fallen creatures. Why?

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Lights Out Louisville – Making migration safer for birds

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Lights Out Louisville – Making migration safer for birds

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Lights Out’ Initiative Launched in New York to Protect Migrating Birds

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Lights Out’ Initiative Launched in New York to Protect Migrating Birds

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‘Lights Out’ Initiative Launched in New York to Protect Migrating Birds

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New York State agencies today announced two initiatives designed to protect and foster increased appreciation for birds - a new ‘Lights Out’ initiative to help protect migrating birds as they navigate night skies, and the launch of the Capital Region segment of the New York State Birding Trail to highlight the State’s world-class and wide-ranging birding opportunities. State buildings participating in Lights Out will keep non-essential outdoor lighting from affecting the ability of birds to migrate successfully, both in the Capital Region and throughout New York.

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17 Iconic Portland Buildings Went Lights Out to Fight Light Pollution

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17 Iconic Portland Buildings Went Lights Out to Fight Light Pollution

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17 Iconic Portland Buildings Went Lights Out to Fight Light Pollution

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On September 15, 17 iconic Portland buildings turned off their unnecessary lights, taking part in the 2017 launch of the Audubon Society of Portland’s Lights Out campaign, an effort designed to encourage Portlanders to save energy, save birds and see stars.

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Lights Out Texas - Dimming Lights for Birds - Documentary

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Lights Out Texas - Dimming Lights for Birds - Documentary

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Lights Out Texas - Dimming Lights for Birds - Documentary

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Guided by starlight, re-routed to death

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Guided by starlight, re-routed to death

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If only birds were ‘puppies’: Lights Out Baltimore tracks 3,000 window collisions since 2018

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In downtown Baltimore, Nicole Hartig and Jon Merryman are on the frontlines of a global problem, collecting data and rescuing birds during peak migration seasons. Their work for Lights Out Baltimore helps raise awareness to prevent avoidable, deadly window strikes.

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The Birds Are Coming - Will the Lights Be Out? - Northern Virginia Bird Alliance

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The Birds Are Coming - Will the Lights Be Out? - Northern Virginia Bird Alliance

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Migration season is approaching fast. Between March 15 and May 31, 100 million birds will pass through northern Virginia, most of them flying at night. The birds can be disoriented by bright lights from tall buildings and sky glow from light pollution. Some crash into the buildings and are injured or die. Other birds fly around the lights, exhausting themselves. It's critical that we take steps to help protect them.

There are three ways you can help protect migrating birds.

Help us talk to building managers. NVBA and other members of the Bird Safe NOVA partnership will be contacting building managers in the Tysons and Reston areas to tell them how important it is to turn lights out between 11 PM and 6 AM during migration season. How effective we'll be will depend on how many people are willing to help. If you'd like to work with us on this project, please email advocacy@nvbirdalliance.org.

Search for birds injured or killed by window collisions. We will work with the Wildlife Rescue League to train volunteers who will walk around tall buildings early in the morning during migration season to document bird deaths from window collisions. Data on bird deaths can be used to help convince building managers to turn their lights out at night. We'll provide training on where to go and what to do and provide business cards with contact information so people can let us know when they find dead birds. Of course, if the bird needs help, call the Wildlife Rescue League at 703-440-0800.

Help build a database of bird collisions. Jeremy Andre, an alumnus of George Mason University, has developed the One Stone Bird Map, a geographic information system (GIS) visualization project designed to track and analyze avian mortality across the DC, Maryland, and Virginia (DMV) area. The project's objective is to shed light on the under-reported issue of bird deaths in urban areas, particularly from window collisions and outdoor cats. You can learn more about the project here.

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The Birds Are Coming - Will the Lights Be Out? - Northern Virginia Bird Alliance

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Migration season is approaching fast. Between March 15 and May 31, 100 million birds will pass through northern Virginia, most of them flying at night.

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‘Lights Out’ seeks to stem bird carnage caused by city skylines

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‘Lights Out’ seeks to stem bird carnage caused by city skylines

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‘Lights Out’ seeks to stem bird carnage caused by city skylines

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During migration season, volunteers comb the pre-dawn streets of cities in search of fallen creatures. Why?

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Night Sky: With Light Pollution Vs. Without Light Pollution

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Night Sky: With Light Pollution Vs. Without Light Pollution

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Night Sky: With Light Pollution Vs. Without Light Pollution

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Witnessing the Night Sky's Hidden Beauty Without Light Pollution😍😍

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Witnessing the Night Sky's Hidden Beauty Without Light Pollution😍😍

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Witnessing the Night Sky's Hidden Beauty Without Light Pollution😍😍

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Where Are the Stars? See How Light Pollution Affects Night Skies | Short Film Showcase

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Where Are the Stars? See How Light Pollution Affects Night Skies | Short Film Showcase

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Where Are the Stars? See How Light Pollution Affects Night Skies | Short Film Showcase

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Do people even care about Light Pollution?

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Do people even care about Light Pollution?

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Do people even care about Light Pollution?

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How artificial light threatens nature | DW Documentary

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How artificial light threatens nature | DW Documentary

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How artificial light threatens nature | DW Documentary

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Residents complain about light pollution - great definition of footcandles

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Residents complain about light pollution - great definition of footcandles

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Too-bright lights at night can affect stargazing, health, wildlife and more

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Tri-County Times | Fenton, MI Hannah Ball Staff Reporter

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Residents complain about light pollution

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Linden — Are the lights in Linden too bright?

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Bat Nebula (IC 1340) – Constellation Guide

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The Bat Nebula (IC 1340) is an ionized region within the larger Veil Nebula, an ancient supernova remnant located in the constellation Cygnus (the Swan).

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Cetus constellation is located in the northern sky. Also known as the Whale, it is one of the largest constellations in the sky.

The constellation was named after Cetus, the sea monster from the Greek myth about Andromeda. In the myth, the princess was sacrificed to the monster as punishment for her mother Cassiopeia's boastfulness. The constellation Cetus lies in the region of the sky called the Water, along with several other constellations with names evocative of water: Eridanus (the river), Aquarius (the water bearer), Pisces (the fish), etc. It was catalogued by the Greek astronomer Ptolemy in the 2nd century.

Cetus is home to the barred spiral galaxy Messier 77 and several well-known stars: Diphda (Beta Ceti), Menkar (Alpha Ceti), Tau Ceti and the famous variable star Mira (Omicron Ceti).
FACTS, LOCATION & MAP
Cetus is the fourth largest constellation in the sky, occupying an area of 1231 square degrees. It lies in the first quadrant of the southern hemisphere (SQ1) and can be seen at latitudes between +70° and -90°. The neighboring constellations are Aquarius, Aries, Eridanus, Fornax, Pisces, Sculptor, and Taurus.

Cetus belongs to the Perseus family of constellations, along with Andromeda, Auriga, Cassiopeia, Cepheus, Lacerta, Pegasus, Perseus, and Triangulum.

Cetus has 14 stars with known planets and contains one Messier object, Messier 77 (M77, NGC 1068). The brightest star in the constellation is Diphda (Beta Ceti). There are three meteor showers associated with Cetus: the October Cetids, the Eta Cetids, and the Omicron Cetids.

The constellation contains eight formally named stars. The star names approved by the International Astronomical Union (IAU) are Axólotl, Baten Kaitos, Diphda, Kaffaljidhma, Menkar, Mira, Mpingo, and Felixvarela.
MYTH
Cetus represents the sea monster from the Greek myth of the princess Andromeda, whose boastful mother Cassiopeia angered the sea god Poseidon and the Nereids (sea nymphs) by claiming that she was more beautiful than any of them.

To appease the sea god and the nymphs, Cassiopeia and her husband, King Cepheus, had to sacrifice their young daughter to Cetus, a sea monster sent by Poseidon to punish the king and queen, or watch the monster ravage their land.

Andromeda was chained to a rock and left to the sea monster, but to her good fortune, the hero Perseus was passing by just as Cetus was about to devour her. Perseus rescued the princess and killed Cetus. He and Andromeda were later married.

Cetus was commonly depicted by the Greeks as a hybrid creature. It had forefeet, huge jaws, and a scaly body like a giant sea serpent. Even though the constellation is also known as the Whale, the mythical creature in the depictions does not in fact look like a whale.
MAJOR STARS IN CETUS Diphda (Deneb Kaitos) - β Ceti (Beta Ceti)
Beta Ceti is the brightest star in the constellation. It has an apparent magnitude of 2.04 and is approximately 96.3 light-years distant.

Beta Ceti is an orange giant belonging to the spectral type K0 III. It has left the main sequence stage of evolution and is on its way to becoming a red giant. With a surface temperature of 4,800 K, the star is slightly cooler than the Sun.

Beta Ceti is known by its traditional names, Deneb Kaitos and Diphda. Deneb Kaitos is derived from the Arabic phrase Al Dhanab al Ḳaiṭos al Janūbīyy, which means "the southern tail of Cetus," and Diphda comes from aḍ-ḍafdaʿ aṯ-ṯānī, which is Arabic for "the second frog." (The star Fomalhaut in Piscis Austrinus is usually referred to as the first frog.)
Menkar (Menkab) - α Ceti (Alpha Ceti)
Alpha Ceti is a very old red giant star, approximately 249 light years distant. The star will eventually eject its outer layers to form a planetary nebula, leaving a large white dwarf remnant. It has an apparent magnitude of 2.54.

The star's traditional name, Menkar, comes from the Arabic word for "nostril." Alpha Ceti is often used in works of science fiction, most notably in Star Trek: The Original Series. Alpha Ceti V was the planet on which Khan and his crew were exiled. In Star Trek: Enterprise, the same planet provided refuge to Humanity after the Xindi destroyed the Earth.
Mira - ο Ceti (Omicron Ceti)
Omicron Ceti, better known as Mira, is a binary star consisting of a red giant and a companion star. The system is approximately 420 light years distant.

Mira A, a red giant belonging to the spectral type M7 IIIe, is an oscillating variable star that serves as a prototype for an entire class of variables, the Mira variables. There are between 6,000 and 7,000 known stars belonging to this group. They are all red giants whose surfaces oscillate in such a way as to cause variations in brightness over periods ranging from 80 to more than 1,000 days.

Mira was the first non-supernova variable star discovered, with the possible exception of Algol in the constellation Perseus, which was confirmed as a variable only in 1667. Mira is believed to be about six billion years old.

The companion star, Mira B, is a high temperature white dwarf that is accreting mass from the red giant. The two form a symbiotic pair, the closest one of its kind to the Sun.

Mira is the brightest periodic variable star that cannot be seen by the naked eye during a part of its cycle. It has a period of 332 days. Its variability was first documented by the German astronomer David Fabricius in 1596. Fabricius believed it was a nova until he saw the star again in 1609. Frisian astronomer Johannes Holwarda, who determined the star's variation cycle, is usually credited for discovering its variability.

It was the Polish astronomer Johannes Hevelius who named the star Mira, meaning "wonderful" in Latin.

The star is shedding a trail of material from its outer envelope. NASA's Galaxy Evolution Explorer space telescope has revealed a tail 13 light years in length, trailing after Mira.
τ Ceti (Tau Ceti)
Tau Ceti is a cool class G (G8.5) dwarf with an apparent magnitude of 3.5. It is one of the nearest stars to our solar system, lying only 11.9 light years away. It has a mass only about 78 percent that of the Sun and is one of the very few stars less massive than the Sun that are nevertheless visible to the naked eye. It is a metal-deficient star with a high proper motion. Its luminosity is equal to only 55% of the Sun's luminosity.

Tau Ceti and Epsilon Eridani in Eridanus constellation were the two nearby stars similar to the Sun that Cornell University astronomer Frank Drake picked for Project Ozma, a pioneering SETI experiment in 1960 aiming to discover intelligent signals from space. Needless to say, there weren't any significant findings.
DEEP SKY OBJECTS IN CETUS Messier 77 (M77, NGC 1068)
Messier 77 is a barred spiral galaxy in Cetus, approximately 47 million light years distant and 170,000 light years in diameter. It has an apparent magnitude of 9.6. It is one of the largest galaxies listed in Messier's catalogue.

Messier 77 was discovered by the French astronomer Pierre Méchain in 1780 and then catalogued by Charles Messier. Méchain originally described the object as a nebula, while Messier and William Herschel described it as a star cluster. The galaxy can be easily found 0.7 degrees east-southeast from Delta Ceti, a fourth magnitude star.

The galaxy has an Active Galactic Nucleus (AGN) which is blocked from view by intergalactic dust. The galaxy's core is a strong radio source. Bernard Yarnton Mills was the first to discover this. He designated the object Cetus A.
NGC 1055
NGC 1055 lies only 0.5 degrees north-northeast of Messier 77. It is spiral galaxy, seen edge-on, approximately 52 million light years distant. It was discovered by the English astronomer William Herschel in 1783.

Next to Messier 77, NGC 1055 is a largest member of a galaxy group that also includes NGC 1073 and several smaller irregular galaxies. It has a diameter of about 115,800 light years. The galaxy is a known radio source.
NGC 1087
NGC 1087 is an intermediate spiral galaxy, approximately 80 million light years distant. It has a very small central bar and a number of irregular features in the disk of material that surrounds it. The galaxy's nucleus is extremely small.

NGC 1087 is located close to NGC 1090, another barred spiral galaxy, but the two are not interacting.
NGC 1073
NGC 1073 is another galaxy in Cetus. It is believed to have an H II nucleus. It has an apparent magnitude of 11.5.
NGC 45
NGC 45 is a barred spiral galaxy, about 32.6 million light years away in Cetus. It has an apparent magnitude of 10.4. The galaxy was discovered by the English astronomer John Herschel in 1835.
NGC 17
NGC 17 is a spiral galaxy in Cetus, approximately 250 million light years distant. It has an apparent magnitude of 15.3.

The galaxy is believed to have formed as a result of the merger of two disk galaxies. It shows recent starburst activity in the core regions and it is still gas rich.
NGC 47 (NGC 58)
NGC 47 is a barred spiral galaxy, approximately 236 million light years distant. It has an apparent magnitude of 13.5.

The galaxy was discovered by the German astronomer Ernst Wilhelm Leberecht Tempel in 1886. It is also known as NGC 58. (The American astronomer Lewis Swift observed the object later and was unaware that it had already been discovered by Tempel.)

The galaxy appears as a small spiral nebula with a bright core.
NGC 1042
NGC 1042 is a spiral galaxy with an apparent magnitude of 14.0.

It is located near another galaxy, NGC 1035, and the two are believed to be physically associated with each other because they have similar redshifts.
NGC 247
NGC 247 (Caldwell 62) is an intermediate spiral galaxy in Cetus, approximately 11.1 million light years distant. It is gravitationally bound to the Sculptor Galaxy (NGC 253) in Sculptor constellation, located in the centre of the Sculptor Group of galaxies, one of the nearest groups to the Milky Way Galaxy.

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Cetus constellation is located in the northern sky. Also known as the Whale, it is one of the largest constellations in the sky. The constellation was named after Cetus, the sea monster from the Greek myth about Andromeda. In the myth, the princess was sacrificed to the monster as punishment for her mother Cassiopeia's boastfulness.

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Autumn's celestial sea: Catch these 'water' constellations in the night sky this fall

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Autumn's celestial sea: Catch these 'water' constellations in the night sky this fall

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Autumn’s celestial sea: Catch these ‘water’ constellations in the night sky this fall

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Autumn officially arrives in the Northern Hemisphere on Tuesday, Sept. 22 at 9:31 a.m. EDT (1331 GMT). And consequently, our evening sky is now one in transition.

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SEE THE CELESTIAL BIRDS OF THE MILKY WAY

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SEE THE CELESTIAL BIRDS OF THE MILKY WAY

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See the Celestial Birds of the Milky Way

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Summer is perfect for bird-watching whether that be in the trees or among the stars of the Milky Way. We explore the celestial birds of the season.

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Heavenly Aviaries - Bird Constellations - Astronomy

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The night sky is full of starry birds. Here is a selection, ranging from the majestic swan to the exotic birds of the southern skies: the peacock, bird of paradise and toucan. There is also an emu whose image appears not in the stars, but in the dark nebulae. - Heavenly Aviaries - Bird Constellations - Astronomy at BellaOnline

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🦅From ancient legends to modern astronomy, delve into the fascinating history of the Aquila constellation.

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Does artificial light interfere with the activity of nocturnal mammals? An experimental study using road underpasses

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Does artificial light interfere with the activity of nocturnal mammals? An experimental study using road underpasses

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Author links open overlay panel

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Light pollution demo - shielded light vs non shielded 

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Light pollution demo - shielded light vs non shielded 

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The Impact of Light Pollution on Fireflies and Nocturnal Animals - Forward Pathway

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The Impact of Light Pollution on Fireflies and Nocturnal Animals - Forward Pathway

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The Impact of Light Pollution on Fireflies and Nocturnal Animals - Forward Pathway

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The Impact of Light Pollution on Fireflies and Nocturnal Animals - fully visualized data of colleges rankings, basic information, admission, graduation, tuition, majors, students, campus safety and more information. - Forward Pathway

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Light Pollution - Lesson Plan — Voyageurs Conservancy

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Light Pollution - Lesson Plan — Voyageurs Conservancy

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Light Pollution - Lesson Plan — Voyageurs Conservancy

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Voyageurs National Park Association is a nonprofit organization dedicated to helping you explore, support, and protect Minnesota’s National Park.

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Dark Sky Lighting: A Solution to Light Pollution | Office of Environmental and Energy Coordination

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Dark Sky Lighting: A Solution to Light Pollution | Office of Environmental and Energy Coordination

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Dark Sky Lighting: A Solution to Light Pollution | Office of Environmental and Energy Coordination

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Fairfax County, Virginia - Page about the Dark Sky conservation movement, dark sky lighting and light pollution

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Southampton Approves Enhanced Dark Skies Legislation

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The Southampton Town Board has approved new Dark Skies rules, introducing stricter guidelines for nonresidential outdoor lighting.

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‘Cool’ white car headlights more likely to dazzle and endanger moths

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‘Cool’ white car headlights more likely to dazzle and endanger moths

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‘Cool’ white car headlights more likely to dazzle and endanger moths

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“Cool” white lights—such as those in modern car headlights—endanger moths by causing them to fly erratically, new research shows. The findings are published in the journal Biology Letters.

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Light Pollution: How it affects the brain -

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Light Pollution: How it affects the brain -

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Light Pollution: How it affects the brain - Remedy Psychiatry, Inc

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In this article, we will explore the intricacies of light pollution and how its effects can disrupt aspects of our health.

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From Songbirds to Dung Beetles, These Animals Can Navigate by Starlight 

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From Songbirds to Dung Beetles, These Animals Can Navigate by Starlight 

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The ability to follow stellar cues is far more common among animals than you might think. But experts warn this could be threatened by light pollution.

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From Songbirds to Dung Beetles, These Animals Can Navigate by Starlight

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The ability to follow stellar cues is far more common among animals than you might think. But experts warn this could be threatened by light pollution.

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Humanity would watch helplessly as space junk multiplies uncontrollably’: has the number of satellite launches reached a tipping point?

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Humanity would watch helplessly as space junk multiplies uncontrollably’: has the number of satellite launches reached a tipping point?

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‘Humanity would watch helplessly as space junk multiplies uncontrollably’: has the number of satellite launches reached a tipping point?

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From chaotic collisions to depletion of the ozone layer, the thousands of satellites in orbit around Earth have the potential to wreak havoc in coming decades. What are the solutions to a growing menace?

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Light pollution from led lighting systems and ways of reducing its environmental consequences

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Light pollution from led lighting systems and ways of reducing its environmental consequences: ISSN 2223-6775 Ukrainian journal of occupational health Vol.20, No 2, 2024https://doi.org/10.33573/ujoh2024.02.138 Light pollution from led lighting systems and ways of reducing its environmental consequences Sakhno T.V.1 , Kozhushko G.M.2, Nazarenko V.I.

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Bird migration is peaking in DC - but light pollution puts them at risk. Here's how to help

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Bird migration is peaking in DC - but light pollution puts them at risk. Here's how to help

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Large numbers of birds are expected to fly over the D.C. area for their fall migration this week, and they are at risk from light pollution. But you can help by simply flipping some switches.

Bird migration is expected to peak through Thursday, meaning tens of thousands of birds will travel through the skies above D.C., according to BirdCast, a website that tracks migration. For example, the website counted 6,100 birds in the skies about midnight Wednesday.

High migration traffic is likely between 11 p.m. Wednesday and 6 a.m. Thursday.

Birds migrate when most people are winding down- and turning on lights. But light from homes, power lines, wind turbines, communication towers and buildings pose a threat to these masses.

Birds are attracted to light, and it can distract them. Sometimes, confused birds fly into buildings at high speed.

Bird deaths are extremely common during migration seasons. Each year, an estimated 365 million to 998 million birds die in building collisions due to light pollution.

You can take precautions to help ensure these birds get to their warmer winter destination.

Tips on reducing light pollution during bird migration season

Here are some tips on how you can help migrating birds:

Be sure to turn off unnecessary lights at night

Use warm-toned bulbs

Put decals on your windows so they're easy for birds to see, according to the National Audubon Society

Write your office or apartment building manager and encourage them to turn out excess lights at night

Search local migration tools to see exactly when birds are expected above your area.

If you find an injured bird, contact a local rescue organization. Animal Help Now maintains a list of organizations.

If you find a bird that died from a window strike, report it, D.C. nonprofit City Wildlife says. Email a picture to lodc@citywildlife.org if you find a bird in D.C. If you find a bird elsewhere, you can report it to the Bird Window Strike Project.

Approximately 15 million birds have migrated this season since August, and many more are expected. Fill up your bird feeders if you'd like to experience this migration event first-hand.

The nocturnal migrants that tend to populate D.C. include the dark-eyed junko, the ruby-crowned kinglet and the golden-crowned kinglet.

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Bird migration is peaking in DC - but light pollution puts them at risk. Here's how to help

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Large numbers of birds are expected to fly over the D.C. area for their fall migration this week, and they are at risk from light pollution. But you can help by simply flipping some switches. Bird migration is expected to peak through Thursday, meaning tens of thousands of birds will travel through the skies above D.C., according to BirdCast, a...

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by Ronald Gibbons, Joseph Cheung, and Paul Lutkevich

Researchers studying the role of illumination in traffic safety make the case for adaptive control systems.

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Ronald Gibbons, Joseph Cheung, and Paul Lutkevich

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Researchers studying the role of illumination in traffic safety make the case for adaptive control systems.

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Our street lighting doesn’t need to be this bad

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Our street lighting doesn’t need to be this bad

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Our street lighting doesn’t need to be this bad

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Most streets are either too bright or too dark. If we have the technology, why are we still over-lighting our streets?

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The system also increases safety on the city’s streets and sidewalks.

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The system also increases safety on the city’s streets and sidewalks.

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LED streetlights help Massachusetts city reach sustainability goals - American City and County

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Cambridge Mass., has partnered with Echelon Corp. for an energy-saving lighting control system that was integrated with the city’s new streetlight infrastructure.

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Five Rules to Minimize Light Pollution from Your Landscape Lighting 

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Five Rules to Minimize Light Pollution from Your Landscape Lighting 

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Low voltage landscape lighting is a great way to add evening functionality to your home landscape, as well as highlight and enhance some of those landscape elements at night. But it's also important to consider whether these light fixtures may be adding to the growing light pollution problem that is impacting our world more and more each day, or to be more exact, impacting each night.

What exactly is light pollution and why is it a problem? The International Dark-Sky Association defines it as: "The inappropriate or excessive use of artificial light - known as light pollution - can have serious environmental consequences for humans, wildlife, and our climate." Light pollution keeps us from having the ability to view the stunning vistas of the night sky that have delighted and inspired our ancestors for millennia prior to the advent of artificial lights. But its not just stargazing that is compromised by nighttime light pollution. Artificial lights can harm wildlife such as insects, migratory birds, turtles and mammals, by disorienting them, distracting them so they are more easily preyed upon, or even disrupting migrations leading to exhaustion or starvation.

Light pollution has grown so much over the recent decades that researchers have concluded that "more than 80% of the world and more than 99% of the U.S. and European populations live under light-polluted skies. The Milky Way is hidden from more than one-third of humanity, including 60% of Europeans and nearly 80% of North Americans. Moreover, 23% of the world's land surfaces between 75°N and 60°S, 88% of Europe, and almost half of the United States experience light-polluted nights." (https://www.science.org/doi/10.1126/sciadv.1600377#T1)

The International Dark-Sky Association lists the components of light pollution as:

Glare - excessive brightness that causes visual discomfort

Skyglow - brightening of the night sky over inhabited areas

Light trespass - light falling where it is not intended or needed

Clutter - bright, confusing and excessive groupings of light sources

The IDA has a list of 5 rules to consider when planning for landscape lighting:
Use light only if it is needed All light should have a clear purpose. Consider how the use of light will impact the area, including wildlife and their habitats. Consider using reflective paints or self-luminous markers for signs, curbs, and steps to reduce the need for permanently installed outdoor lighting. Direct light so it falls only where it is needed Use shielding and careful aiming to target the direction of the light beam so that it points downward and does not spill beyond where it is needed. Light should be no brighter than necessary Use the lowest light level required. Be mindful of surface conditions, as some surfaces may reflect more light into the night sky than intended. Use light only when it is needed Use controls such as timers or motion detectors to ensure that light is available when it is needed, dimmed when possible, and turned off when not needed. Use warmer-color lights where possible. Limit the amount of shorter wavelength (blue-violet) light to the least amount needed.
And the International Dark-Sky Association has this summary that is a good mantra to consider if you want to keep your outdoor lighting from causing unnecessary light pollution: "Light where you need it, when you need it, in the amount needed, and no more."

Our landscape lighting plans don't have to make the light pollution crisis much worse than it already is. We can use landscape light judiciously around our properties. We can use fewer up-lights and more down-lights. We can keep the light level low and the light color warm. And we can use timing devices to turn off the brighter landscape lights when the pool party or garden fete is over, the guests have gone home, and we've gone inside for the night.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
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Five Rules to Minimize Light Pollution from Your Landscape Lighting - Lot-Lines

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Low voltage landscape lighting is a great way to add evening functionality to your home landscape, as well as highlight and enhance some of those landscape elements at night. But it's also important to consider whether these light fixtures may be adding to the growing light pollution problem that is impacting our world more and [...]

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What is ecological light pollution? Ecological light pollution arising from artificial light at night (ALAN) is any non-natural (anthropogenic) source of light in the environment that alters natural light regimes and disrupts ecology

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Four ways to curb light pollution, save bugs: Insects have experienced global declines. Flipping the switch can help

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Four ways to curb light pollution, save bugs: Insects have experienced global declines. Flipping the switch can help

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Artificial light at night negatively impacts thousands of species: beetles, moths, wasps and other insects that have evolved to use light levels as cues for courtship, foraging and navigation.

Writing in the scientific journal Biological Conservation, Brett Seymoure, the Grossman Family Postdoctoral Fellow of the Living Earth Collaborative at Washington University in St. Louis, and his collaborators reviewed 229 studies to document the myriad ways that light alters the living environment such that insects are unable to carry out crucial biological functions.

"Artificial light at night is human-caused lighting -- ranging from streetlights to gas flares from oil extraction," Seymoure said. "It can affect insects in pretty much every imaginable part of their lives."

Insects and spiders have experienced global declines in abundance over the past few decades -- and it's only going to get worse. Some researchers have even coined a term for it: the insect apocalypse.

"Most of our crops -- and crops that feed the animals that we eat -- need to be pollinated, and most pollinators are insects," Seymoure said. "So as insects continue to decline, this should be a huge red flag. As a society of over 7 billion people, we are in trouble for our food supply."

Unlike other drivers of insect declines, artificial light at night is relatively straightforward to reverse. To address this problem, here are four things that Seymoure recommends:
1. Turn off lights that aren't needed
The evidence on this one is clear.

"Light pollution is relatively easy to solve, as once you turn off a light, it is gone. You don't have to go and clean up light like you do with most pollutants," Seymoure said.

"Obviously, we aren't going to turn off all lights at night," he said. "However, we can and must have better lighting practices. Right now, our lighting policy is not managed in a way to reduce energy use and have minimal impacts on ecosystem and human health. This is not OK, and there are simple solutions that can remedy the problem."

Four characteristics of electrical light matter the most for insects: intensity (or overall brightness); spectral composition (how colorful and what color it is); polarization; and flicker.

"Depending on the insect species, its sex, its behavior and the timing of its activity, all four of these light characteristics can be very important," Seymoure said.

"For example, overall intensity can be harmful for attracting insects to light. Or many insects rely upon polarization to find water bodies, as water polarizes light. So polarized light can indicate water, and many insects will crash into hoods of cars, plastic sheeting, etc., as they believe they are landing on water."

Because it is impossible to narrow down one component that is most harmful, the best solution is often to just shut off lights when they are not needed, he said.
2. Make lights motion-activated
This is related to the first recommendation: If a light is only necessary on occasion, then put it on a sensor instead of always keeping it on.
3. Put fixtures on lights to cover up bulbs and direct light where it is needed
"A big contributor to attraction of light sources for most animals is seeing the actual bulb, as this could be mistaken as the moon or sun," Seymoure said. "We can use full cut-off filters that cover the actual bulb and direct light to where it is needed and nowhere else.

"When you see a lightbulb outside, that is problematic, as that means animals also see that light bulb," he said. "More importantly, that light bulb is illuminating in directions all over the place, including up toward the sky, where the atmosphere will scatter that light up to hundreds of miles away resulting in skyglow. So the easiest solution is to simply put fixtures on light to cover the light bulb and direct the light where it is needed -- such as on the sidewalk and not up toward the sky."
4. Use different colors of lights
"The general rule is that blue and white light are the most attractive to insects," Seymoure said. "However, there are hundreds of species that are attracted to yellows, oranges and reds."

Seymoure has previously studied how different colors of light sources -- including the blue-white color of LEDs and the amber color of high pressure sodium lamps -- affect predation rates on moths in an urban setting.

"Right now, I suggest people stick with amber lights near their houses, as we know that blue lights can have greater health consequences for humans and ecosystems," Seymoure said. "We may learn more about the consequences of amber lights. And make sure these lights are properly enclosed in a full cut-off fixture."

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insects (including butterflies); behavioral science; trees; pests and parasites; pollution; environmental issues; atmosphere; water

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Four ways to curb light pollution, save bugs: Insects have experienced global declines. Flipping the switch can help

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Artificial light at night negatively impacts thousands of species: beetles, moths, wasps and other insects that have evolved to use light levels as cues for courtship, foraging and navigation. Scientists reviewed 229 studies to document the myriad ways that light alters the living environment such that insects are unable to carry out crucial biological functions.

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Streetlights are influencing nature-from how leaves grow to how insects eat

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Streetlights are influencing nature-from how leaves grow to how insects eat

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The steady glow from streetlights is changing the texture of tree leaves, making them less appetizing to insects, according to new research from China.

Light pollution and fog combining to blur a New York City skyline at night. Light pollution is disrupting nature, and a new study found artificial light even made tree leaves less appetizing to insects.

Photograph by Jim Richardson, Nat Geo Image Collection

Insects behave differently when there's light at night: artificial light hinders firefly communication and reproduction, and some insects may become more visible to predators like bats, or be attracted to lights that can kill them.

Researchers based at the Chinese Academy of Sciences were curious about how light might affect relationships between insects and plants. They noticed tree leaves in cities typically showed fewer signs of insect damage than those outside of cities, so they analyzed leaf samples from trees throughout Beijing.

A street lamp shines brightly during a rainstorm in China. A study of trees in Beijing recently found that trees growing under bright artificial light produced tougher leaves.

Photograph by xijian, Getty Images

Focusing on two common street trees-the Japanese pagoda and green ash tree-at 30 sites spaced apart among main roads illuminated at night, the researchers measured brightness and collected leaves. They evaluated almost 5,500 leaves for size, toughness, and levels of nutrients and chemicals, and analyzed them for signs of insects.

Examining leaves' composition and characteristics can tell scientists a lot about how that plant is using resources. Plants grow differently depending on factors in their environment.

"Plants distribute their limited resources (such as nutrients, water, and energy) among various functions like growth, reproduction, and defense," says Ellen Cieraad, plant ecologist at Nelson Marlborough Institute of Technology in New Zealand, in an email. "Depending on the environment, it makes sense to invest in different types of functions." If there are a lot of herbivores around, for example, plants may prioritize defending against being eaten-with thorns, unappetizing chemicals, or tougher leaves.

And for both species of trees the researchers studied, more artificial light in a given area meant tougher leaves. And the tougher the leaf, the less evidence of hungry insects. In areas with the most intense light, leaves were more likely have no signs of insect predation.

A cyclist rides through Primrose Hill in the early evening in London, 2015. Artificial light can cause profound changes in nature, disrupting circadian rhythms and photosynthesis.

Photograph by Peter Nicholls, Reuters/Redux

What do tougher leaves mean for urban environments?

While the researchers from the new study don't fully understand why plants are reacting to streetlights in this way, they hypothesize that trees under artificial light at night might be extending their photosynthesis cycle. Since plants use light for growth, explains Shuang Zhang, biologist at the Chinese Academy of Sciences and author of the paper, artificial night light could be unnaturally increasing the time trees spend on photosynthesis.

Scientists don't fully understand how plants will respond and adapt to the change, says Cieraad.

The type of light also affects how plants use resources: for example absorbing the red light from sunlight can make plants develop tougher leaves, says Cieraad, but these mechanisms probably work differently for artificial red light at night. So something about Beijing's streetlights could be making the trees in this new study allocate more resources to chemical compounds that make leaves tougher.

This research needs to be expanded to other plant species, says Zhang. "If artificial light at night also makes the leaves of other species tougher, this would be bad news for insects," says Zhang.

Changes in plants, and in interactions between plants and animals, can significantly impact the entire urban ecosystem.

A poor diet might cause herbivorous insects die off, resulting in fewer insects that eat those herbivorous insects, and fewer insect-eating birds, and so on up the food chain.

Beyond forming a crucial link in food webs, herbivorous insects are sometimes pollinators and contribute to biodiversity. They also eat decaying plants, helping to break down leaves and returning nutrients to soil. In cities, healthy soil and healthy plant life supported by insects are good for humans. Plants in cities provide shade and mitigate heat trapped in cities.

To minimize the negative impacts of light at night, Zhang recommends simply reducing light intensity. The study found a linear relationship between brightness at night and how much leaves were eaten by insects, so just reducing light intensity could make leaves more appealing to insects.

In cities we should focus on only lighting what and when it is needed, says Cieraad. Motion sensors could also help, as could shields for streetlights so light doesn't spill into surrounding areas.

At home, biologists recommend turning off lights that aren't needed at night, using motion activated lights, choosing fixtures that direct light only where it's needed, and using amber-colored lights near homes which appear to be the safest for insects.

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Streetlights are influencing nature-from how leaves grow to how insects eat

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The steady glow from streetlights is changing the texture of tree leaves, making them less appetizing to insects, according to new research from China.

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Want to help wildlife? Turn off your lights.

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Want to help wildlife? Turn off your lights.

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Look for a constellation in the glow of a city, and at best you might see a star or two. That's because light pollution is turning night into day in 80 percent of the world.

The day to night cycle is an essential part of nature, telling animals when to emerge to hunt, forage, migrate, and mate. When artificial light disrupts those natural light cues, wildlife from bugs to birds, and even plants, are seriously impacted.

It's a problem getting worse every year, but there are simple solutions to help wildlife and restore our night sky view, experts say.

"When we look at the sky and we can't see the stars, it's a sign that our lighting is poorly designed and wasteful," says Christopher Kyba, a physicist at the GFZ German Research Center for Geosciences.

Some communities are rethinking rules for lighting at night, starting with simple changes to reduce light pollution coming from individual homes.

How light pollution harms the environment

A report from last year examined over 160 species of plants, fish, mammals, and insects to understand how our artificial lights are changing ecosystems. Researchers found that animals look to light via the rising and setting of the sun and moon to determine when to emerge from their hiding places to hunt, forage, migrate, and mate. All manner of wildlife is affected-for example, some bugs can be more easily preyed on and some birds fly off course.

"For all of evolutionary history there was a stable pattern-any animal or plant can anticipate day and night," says Kyba. "But when we add a bunch of artificial light, obviously that's going to mess things up."

Fireflies use light to signal to potential mates at night. But city and suburban lights outshine these cues at alarming rates. One study published in 2020 suggested light pollution, along with habitat loss and pesticide use, could put some of the world's 2,000 different firefly species at risk of going extinct.

Birds are also easily disoriented by bright city lights and frequently die from colliding into bright buildings reflecting the sun and shining artificial light at night. Even dim lighting far from the city may impact their health.

A study of zebra finch birds found chemical markers of stress in birds exposed to dim lighting in a lab after just three weeks, but scientists don't yet know what that means for bird health long term, says Valentina Alaasam, a study author and biologist at the University of Nevada, Reno.

And while birds and insects are often highlighted as light pollution victims, artificial light impacts all animals, says Kyba. Even plants are disrupted by light cues.

Turn off, dim, and shield your lights

Unlike removing pollution from the air or water, light pollution can be eliminated immediately. Reducing light pollution can be as simple as turning off the lights, installing motion sensors that limit when lights are on, or adding dimmers that reduce the light coming from a single bulb.

"The best part of a lot of these [solutions] is they save everyone money," says Alaasam. "If you can turn off lights more often, it saves electricity and [reduces carbon emissions] and it's kind of a win-win."

Energy efficient LED light bulbs are cheaper and longer-lasting than their incandescent predecessors, but their widespread adoption has caused problems for wildlife. LED bulbs produce a short-wave blue-tinted light that attracts more insects and birds and disrupts circadian rhythm in mammals. But bulbs with yellow-tinted filters can minimize these impacts.

"The kind of light we use really matters," says Alaasam. "For birds, if you use a warmer, yellower hue, you don't see nearly as many effects."

Shielded coverings for street lamps and outdoor lights help concentrate light directly down to where we need it, preventing it from leaking out and up.

Simply closing your blinds and curtains can also help prevent artificial light from shining into the environment. One study looking at two decades-worth of bird collisions in Chicago found that reducing light leaking out of windows by just half could reduce bird collisions by 60 percent.

Cities going dark

Every year, light pollution increases-by as much as 10 percent, according to one study.

While individual changes to home lights can help local wildlife, communities working together can have the biggest impact.

"Lighting decisions are made by millions of people," says Kyba. "To make real progress you have to get all those people on board."

Some communities are showing what those social changes might look like. The entire island country of New Zealand is currently working to meet light pollution standards; and the Pacific island country of Niue was the first country to become a certified International Dark Sky Sanctuary in 2020.

(Read more about New Zealand's quest to become a "dark sky nation.")

In 2019, France imposed a new law setting strict limits for how and when light shines at night. In the U.S., the National Audubon Society's Lights Out program encourages cities from San Francisco to New York to reduce their nighttime lights during periods when migratory birds are passing through. Dimming bright city lights for as little as 30 minutes can prevent fatal bird collisions, according to a 2017 study.

If advocating for policy changes feels daunting, start small, says Kyba.

"When a light is bothering you or you think it's a problem, it's worth complaining," he says. "Often, there are very simple fixes that don't cost very much money and can basically solve the problem."

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Want to help wildlife? Turn off your lights.

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It's not just about seeing the stars. Bright city lights disorient animals like birds, leading to fatal collisions and potential long-term damage to their health.

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Garden lighting: effects on wildlife / RHS Gardening

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Garden lighting: effects on wildlife / RHS Gardening

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The breeding success of glow worms is adversely affected by artificial lighting
Bats show disrupted feeding patterns in lit areas
Robins extend their activity period in artificial light, feeding longer and singing in the middle of the night
Moths and nocturnal-flying migrating birds can be disorientated by light sources and urban areas

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Garden lighting: effects on wildlife / RHS Gardening

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Night-time lighting either from security lights or decorative garden lighting illuminate our garden spaces after dark, but what about the effects on wildlife?

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How Light Pollution Impacts Wildlife How You Can Help

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How Light Pollution Impacts Wildlife How You Can Help

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How Light Pollution Impacts Wildlife & How You Can Help

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From cougars and bats to butterflies and sea turtles, wildlife are increasingly threatened by light pollution, but simple solutions can help

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All of the effects of artificial light are considered in this campus program

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Committee for the Protection of Astronomy and the Space Environment (COMPASSE)

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Campus SHINE program​ - Committee for the Protection of Astronomy and the Space Environment (COMPASSE)

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Most colleges and universities have accumulated their outdoor l…

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UAB Light Pollution is Being Tackled Through New Lab, Campus SHINE

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UAB Light Pollution is Being Tackled Through New Lab, Campus SHINE

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UAB Light Pollution is Being Tackled Through New Lab, Campus SHINE

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By Micah Hardge | UAB News The University of Alabama at Birmingham is addressing light pollution via the Campus Safe and Healthy Illumination for the Nighttime Environment at UAB. Light pollution i…

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Darkness was falling at Kitt Peak National Observatory outside Tucson, Ariz. At this hour Michelle Edwards, the observatory's associate director, would usually be inside prepping for a night on the telescope. But on this evening last December she stood alongside me in the twilight, watching two worlds collide. As the stars came out, electric lights dotting the landscape below turned on, too, leaving a diminished Milky Way arcing above the brighter civilization. "Holy crap," Edwards said, taken aback by the enormous city glow.

Tucson was a bright bubble eating the eastern sky and the shoulder of Orion. A snake of lesser lights-Interstate 10-wriggled out from the glow, winding 100 miles north toward the glare of Phoenix. To the south, across the Mexican border, loomed another luminous half-circle from the lights of Nogales.

All that light is an existential threat to high-grade stargazing on Kitt Peak. Over the decades astronomers have taken urgent steps to slow or even reverse its spread. For them, the boundary of each glowing dome was a battle line, expanding or shrinking with each skirmish won or lost; the imperfect darkness overhead was a testament to local policy and millions of collective actions-or collective shrugs and proliferations of gleaming billboards and streetlights.

Yet the glow keeps spreading. Under skies so filled with stray photons, it takes twice as long to resolve an astronomical target as it typically would, one Kitt Peak astronomer told me a few hours after sunset. Intense wildfires linked to global warming (such as one that swept the summit half a year after my visit) may pose more obvious risks to the telescopes there, but the subtle, pernicious effects of ever brighter nights could eventually become an even bigger threat to astronomy.

Species spiraling into oblivion, a few extra parts per million of carbon dioxide in the air, sea life gobbling up microplastics-many of our era's ecological calamities are hard to see with unaided eyes. Not so with light pollution, even though astronomers looking through telescopes may have been the first to really notice it. Its impacts are not limited to astronomy, of course. Over the past decade biologists have discovered that wasteful nighttime lighting drastically disrupts animals, plants and the ecological relationships that knit the world together. These effects reach across entire regions of the globe, far outside of cities. "You need to think about it much more like we might think about plastic pollution or some of the climate change effects," says Kevin Gaston, a prominent U.K.-based conservation biologist at the University of Exeter.

Researchers still maintain that we can reduce light pollution without much sacrifice. As new research reveals the scope of the problem, possible fixes become clearer as well. Light pollution is something we can understand and manage, like smokestack emissions or factory wastewater. The sooner we act, the better. Satellite measurements suggest that more than three in five Europeans and four in five North Americans live under skies too light-swamped to allow them to see the Milky Way. Other analyses show Earth's artificially lit surface area bloating outward by about 2 percent a year, transforming the remaining map of true night into Swiss cheese. And although recent LED technology has made lighting cheaper and more energy-efficient than ever, consumers don't seem to be pocketing those savings and reducing carbon emissions. Instead humanity seems to be switching on even more lights.

It doesn't have to be this way. Dark, star-filled skies can once again become the rule rather than the exception, easing the burden on already struggling ecosystems while restoring some celestial wonder into ordinary human lives. Legislation aiming to achieve as much is already being drafted on multiple continents. Any solution, however, depends on questions more social than scientific: Can we sustain the necessary research to properly define and address light pollution? How much nighttime lighting do we really need? And most crucially, maddeningly-does anyone care?

To give scientists and the rest of us some credit, it has always been hard to assess the ecological implications of bathing the world in an eternal false twilight. To some creatures, a lamp is a siren call; to others, it's a repulsive force field. Light's timing, wavelength, direction and intensity, as well as the eyes of the beholder, all matter, and unlike mercury in tuna or DDT in bald eagles, photons don't leave behind a lasting measurable chemical trace. Taken together, though, studies on at least 160 species provide ample evidence that artificial lights send the natural world a bewildering array of ill-timed signals-Wake up! Hide! Hunt! Fly this way! Change your metabolism!

One morning in May of last year, I drove out to a cattle farm in rural North Carolina to meet Murry Burgess, a graduate student at North Carolina State University who had strung up little Christmas lights over swallow nests built in the rafters of a barn. She went up on a ladder, pulled out what looked like squirmy, stubble-feathered dinosaurs one by one, and subjected each chick to a battery of tests while clutching it gently in her warm palms. The parents didn't know to move their nests away from the lights, she said, and the light took a toll on their babies' bodies. Compared with neighboring chicks growing up under no lights, coming of age under just one tiny bulb had made these birds stunted and underweight. "It's crazy how light goes all the way in deep into their cells," Burgess told me.

What harms individual baby barn swallows also operates on the scale of entire species, even ecosystems. Offshore, artificial light can cause reef-building corals that grasp toward the surface to stop spawning all at once, turning what should be synchronized explosions of fresh life into useless, mistimed puffs of eggs and sperm. In the U.S. alone, somewhere between several hundred million and one billion birds die every year after thwacking into windows, many of them beckoned by interior lights.

Insects especially are facing dire consequences. Moths keep flapping into lightbulbs for reasons scientists still don't quite understand. Cricket calls are becoming decoupled from the rhythms of night and day. In the British countryside, research shows caterpillar populations plummeting in roadside hedgerows illuminated by LED streetlights. Light pollution is almost certainly hastening the so-called insect apocalypse, the planet's declining portfolio of bug biomass, although little research has focused on this grim end point.

Light pollution ripples through multiple domains of life. In one 2017 experiment, scientists with night-vision goggles watching cabbage thistle plants confirmed that ambient light deterred nocturnal pollinating insects from making their rounds. Daytime pollinators couldn't make up the deficit, so the plants bore less fruit, suggesting that the effects of brightening nights could eventually show up in supermarket aisles. And while nocturnal light can lead the insects we like to lose conviction, it can fill those we despise with passionate intensity: the mosquito Aedes aegypti, which causes a staggering 400-million-odd infections such as dengue and Zika a year, seems encouraged to bite more in the presence of artificial light, as does another mosquito species that spreads West Nile virus.

Such observations used to be documented one organism at a time in specialist journals, unconnected to a broader research program. But in the late 1990s a pair of grad students and self-described environmental "troublemakers" in Los Angeles began building up a dossier of these kinds of stories. Catherine Rich, a lawyer turned ecologist-in-training, got accepted to several Ph.D. programs, but when she went looking for an adviser who would let her study the effects of light pollution on wildlife, she found no takers. "I would hear things like 'you might not get any results,'" she says. But Rich and her now husband Travis Longcore stuck with the issue and organized what would prove to be a seminal academic conference on the subject.

In their 2002 conference, a 2004 review paper and a subsequent book, Longcore and Rich steered clear of another, parallel field of research-the ongoing exploration of what living in a brighter outdoors and brighter-still indoor world does to human health. (We know light exposure at night is associated with myriad problems, ranging from the obvious, like sleep disruption, to the more surprising, like higher breast cancer risk, but it isn't clear yet how much of this is from outdoor light pollution versus our glowing screens and indoor fixtures.) Even so, journalists and the public began to pick up on the idea that light pollution was real pollution, ecologically speaking. By 2011 high-powered European ecology laboratories such as Gaston's picked up the topic and began cranking out their own results and meta reviews of the literature. As of this year, Longcore and Rich's review paper has been cited more than 1,500 times.

Many of these results involve the easiest kind of light pollution to picture: a single, intense light source shining at you with the harsh glare of LED headlights on a new-model SUV. More recently, however, others have focused on the subtler, more encompassing light-bubble effect I saw from Kitt Peak. The latest, most painstaking ecological findings show that these levels of ambient light pollution have biological consequences, too, even with no specific light sources in sight.

A series of recent experiments, conducted in tanks and under domes bobbing in a German lake, showed that bright skies alone can cause sagging levels of melatonin-a hormonal messenger of darkness-and alter reproductive hormones in Eurasian perch. A separate paper last year showed that whiter nights disoriented dung beetles in South Africa, which look toward the Milky Way to guide themselves in the humble but essential task of burying poop in the savanna. Yet another 2021 study, led by Longcore, showed similarly low thresholds of light on stretches of California beach can prevent plovers from roosting and fish called grunion from throwing themselves ashore to spawn.

All this matters because domes of light from skyglow are visible for hundreds of miles across state and international borders, and studies show they lure migratory birds and insects at regional scales. Even in the rare corners of the planet these domes haven't yet reached, organisms already seem attuned to the faintest changes in lighting. Over winter in the Arctic Ocean, for example, plankton rise and fall each day despite the sun never breaching the horizon. Artificial light from fishing or mining could also scramble that system.

There is no real, organized "pro-skyglow" opposition on the other side of all this funneling money to politicians or pumping out contrarian studies. The problem, scientists assert, is that current lighting trends are driven by unquestioned development and millions on millions of oblivious human decisions. Setting aside regions left in the dark by poverty and neglect, precious few communities have managed to slow down light's advance.

Two weeks before my sojourn at Kitt Peak, I stood shivering in the late-night chill beneath the ponderosa pines around Lowell Observatory in Flagstaff, gazing up at a lunar eclipse. As Earth's shadow slid across the face of the moon, the black of bare sky deepened, and the stars popped brighter, as if a photo editor were fiddling with the vista's contrast levels.

The most memorable part of the whole experience, though, was the downward view overlooking Flagstaff. Almost no illumination besides individual stoplights shined back up. You could blink and convince yourself you were overlooking a sleepy coastal hamlet, not a mountain town of more than 75,000 hoping to snag tourists on their way to the Grand Canyon. It looked like a little corner of modernity had somehow taught itself to close its eyes and fall asleep.

To date, the most successful defenses of dark skies have been mounted in places where astronomers could rally around facilities with economic value. In 1958, around the same time Rachel Carson got the tip that spawned Silent Spring and modern environmentalism, astronomers at Lowell Observatory began to worry about spinning searchlights used in advertising spoiling their view of the sky. In response, Flagstaff put the world's first light-pollution ordinance on the books. Arizona-not exactly a place famous for collectivist, big-government policies-has been the heartland of the dark sky movement ever since.

Two years earlier, a few hundred miles to the south, astronomers and tribal guides from the surrounding Tohono O'odham nation had ridden on horseback to the top of Kitt Peak, exchanging Western and Indigenous star stories by a campfire at the summit. Soon the federal government leased the land from the tribe in perpetuity, and bigger and better telescopes bloomed on the mountaintop.

As light pollution in nearby Tucson ballooned, Kitt Peak astronomers found allies such as Tim Hunter, a doctor who had grown up seeing the Milky Way through elms in the Chicago suburbs, then watched helplessly as artificial light dimmed the galaxy just like Dutch elm disease rotted the trees. Together Kitt Peak astronomer David Crawford and Hunter formed the International Dark Sky Association (IDA) in 1988, hoping to build a broader coalition that included their allies in Flagstaff.

Over the years, as advocates watched darkness retreat, the tools and techniques required to track it advanced. Light-pollution modeling progressed from pen-and-paper equations to computerized ray-tracing simulations. Sophisticated wide-angle cameras made it easier to measure skyglow from the ground, and satellite images started showing spidery webs of light spreading across the globe. The general trend was, and remains, dismal: the better researchers can study the problem, the worse it appears to be.

The IDA and its affiliated researchers reject the assumption that light pollution must intensify as cities grow. Usually crime prevention is the municipal excuse for banishing the night. But how well does this work? Perhaps the most definitive evidence that light suppresses crime comes from an experiment begun in 2016 in which criminologists lugged nearly 400 basketball hoop-sized lighting towers into public outdoor spaces in New York City housing developments. Powered by their own portable fuel generators, the blue-white fixtures were left on from sunset to sunrise-and outdoor crimes around the light towers at night dropped by about 45 percent.*

But dark sky researchers point out that these towers were far brighter than mere streetlights. They also note the ethically dubious nature of any anticrime policy that relies on subjecting majority-minority communities to prison yard-esque floodlights all night long. Indeed, across the continental U.S., the burden of light at night, like other known pollutants, falls harder on less powerful groups: according to a 2020 study from researchers at the University of Utah, Black, Hispanic and Asian American neighborhoods tend to be about twice as illuminated as white ones.

Road safety is another common rationale for the proliferation of lights at night. But here, too, scientists argue that brightness standards are driven by convention, not science. In 2018 lighting researchers from England and the U.S. scanned regulations in Europe and North America. "There appears to be little, if any, credible empirical support for light levels recommended in much current road lighting guidance," they concluded.

Other lighting choices come down to industries and individual people, many of whom remain unreached or unmoved by the issue. Spend any time in dark sky circles, and you'll hear talk of a curse: a moment of revelation, of veil lifting, when you suddenly see bad, wasteful lighting and then can't unsee it. (Mine came on a walk in my Raleigh, N.C., neighborhood, when I realized a richer, whiter "historic" stretch of blocks had dimmer amber streetlights, and the adjacent historically Black neighborhood had harsher white fixtures.)

Many activists have also taken that curse as a call to action. The day after watching the lunar eclipse in Flagstaff, I sat down with Chris Luginbuhl in the city's Dark Sky Brewing Company. Playing along, he ordered a "Circadian Rhythm." That on-the-nose brew had run out, though, so he settled for a brown ale.

Luginbuhl, a former astronomer at the nearby U.S. Naval Observatory who has worked to protect Flagstaff's skies for four decades, knows the field of dark sky science and its progress better than almost anyone. He and his coalition are "like the John Muir character," one colleague told me, "kind of nutty but superpassionate." Streetlights here are a dim orange because, as Luginbuhl explains, blue-tinged light is more disruptive to most animals at night (humans included), as well as to nearby astronomical observatories. That's because bluer, shorter-wavelength photons scatter more readily in the air, creating a localized fog of light.

Nursing his beer, Luginbuhl praised his town as a paragon, a proof of concept that other communities could emulate. In 2017 the U.S. National Park Service deployed an ultrasensitive panoramic camera outside both Flagstaff and the similarly sized city of Cheyenne, Wyo., which does not have comparable dark sky ordinances. Cheyenne was 14 times brighter than Flagstaff, and the bubble of trapped light around it was eight times bigger. Luginbuhl says his strategy has been simply to show people the stars and convince them that being able to see them is a matter of choice-that there is no zero-sum conflict pitting growth against wilderness. "Do I think that stars will win out over light? Almost every time," Luginbuhl says. "They're mind-bending, and everybody needs to have their minds bent."

In the spring of 1942 Nazi Germany sent U-boats slinking across the Atlantic to prey on American shipping lanes. Cargo sank by the ton, drowned bodies washed ashore, and it soon became clear that the submarine gunners were picking off ships at night by watching for their dark silhouettes against skyglow over the coast.

Elected officials and chambers of commerce in cities such as Miami were pressured to dim lights and turn off glitzy outdoor displays. Clearly, this light pollution had literal life-or-death stakes. For three months, though, community leaders dragged their heels, subverting a collective response, citing economic concerns. The carnage offshore ultimately moved President Franklin D. Roosevelt to issue an executive order that compelled coastal blackouts, and U-boat attacks waned as defensive patrols were stepped up and communities for many miles inland restricted their use of nighttime lights, even taping over car headlights. All this is within living memory: my late grandmother, a teenager at the time, told stories about how serious it felt to keep the lights off that summer in Wrightsville Beach, N.C.

"It's like, oh, my God," says Christopher Kyba, a physicist and dark skies advocate at the GFZ German Research Center for Geosciences in Potsdam. Even back then, "the U.S. government knew how to control skyglow! We're not waiting for some breakthrough technology." Smarter, more data-driven guidance on unnecessary lighting can exist; presumably the collective will to act on it can, too.

Barring that, it's easy to imagine the planet's wealthier regions cranking out ever more wasted light powered by wasted carbon, evaporating the remnants of true night like water from a drying lake bed and subjecting life on Earth to an additional stressor in a world increasingly full of them. Or-and this is also eminently possible-we can come to notice wayward light as we would a neighbor's garden sprinkler accidentally set to water the street. With enough restraint, the Milky Way can shine once more above bustling human communities.

Pressure to dim the lights is building. Multiple U.S. states are reviewing proposed dark sky-friendly legislation. Campaigns to turn off lights during bird migration season are spreading all over the country; in Texas cities such as Dallas and Houston, for example, more than 100 downtown buildings dimmed their lights this past spring. And since 2001, when the IDA started recognizing places where dark skies are being preserved-Flagstaff, of course, was first on the list-nearly 200 such sites have been certified around the globe.

Even bolder policies are unfolding in Europe. In France, a law passed in 2019 bars businesses from leaving decorative lights and signs illuminated all night. In Germany, which has developed a legal action plan to reverse insect declines, controlling light pollution is considered to be a major goal. On the technology front, LED makers, sensing an unmet need, are adding dark sky-friendly, downward-pointing, long-wavelength fixtures to the market. And the Holker Lab in Berlin-the ones behind those fancy lake experiments on skyglow-have developed prototype lights that don't emit the wavelengths disruptive to most insects. "The crazy thing about this problem," ecologist Jesse Barber of Boise State University told me, echoing a sentiment common throughout dark sky circles, "is it's so damn fixable."

It's hard to care for what you've never seen. The Milky Way-a glitter bomb of awe that all our grandparents and all preceding humanity could witness whenever they wanted-is the biggest reward for limiting light pollution. But unlike residents of the American West, who can summon its appearance with modest reductions in light, people in the more densely populated, brighter eastern U.S. can't gain even a subpar view of our galaxy without hours-long drives to isolated pockets of darkness. There are other perspectives to consider, though.

Recently I learned of a quiet little wonder left in my own world: a species of ghost firefly was discovered haunting old pine stands near my home in the Piedmont of central North Carolina. The males of this species keep their lights on for up to 30 seconds at a time, scrawling faint, floating messages, and the females sit still below, gleaming back up silent, greenish answers.

In 2021 citizen scientists spotted populations of this firefly in some of the state's most urbanized counties, where, of course, they had been all along. They easily could have been paved over to extinction before anyone noticed. The entomologist searching for the species, Clyde Sorenson of North Carolina State, even stumbled onto a population in his very own backyard. "I've been living there for 25 years," he told me, sheepishly.

Desperate for a little reenchantment myself, I pulled up in his driveway one evening this past spring. We set out into the adjoining woodlot, wearing headlamps and crunching through leaves as a bullfrog bellowed in the background. This being a new species, we didn't know the exact time of year to expect it or the right weather. We did know darkness was necessary.

Fireflies, obviously, are sensitive to levels of light, the medium in which they communicate. Studies show ambient light pollution obstructs firefly courtship to the extent that some species don't even bother to try. As we walked that night, errant rays-from our phones, streetlights through the trees, the neighbor's security floodlight-kept needling their way back in, illuminating all the fireflies' likely hiding spots.

But then we saw three huddled females scintillating like misplaced stars, glowing from a shadowy crevice of glare-blocking leaf litter. Their bodies were the size of grains of rice. I leaned in close, and each firefly's star divided into two emerald dots, two side-by-side light organs cranking out their own feeble wattage into the scattered remnants of the dark-a broadcast they continued for about half an hour, until that evening's shift ended, and they winked out.

*Editor's Note (9/29/22): This sentence was edited after posting to correct the description of when the blue-white fixtures were left on.

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The Sky Needs Its ‘Silent Spring’ Moment

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Darkness was falling at Kitt Peak National Observatory outside Tucson, Ariz. At this hour Michelle Edwards, the observatory's associate director, would usually be inside prepping for a night on the telescope. But on this evening last December she stood alongside me in the twilight, watching two worlds collide.

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Light is the Next Ocean Pollutant of Concern

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Light is the Next Ocean Pollutant of Concern

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Light is the Next Ocean Pollutant of Concern

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For years the world has largely ignored an insidious pollutant humanity has been carelessly throwing into the ocean: light.Newly hatched turtles can…

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Black History Month: A History of Forced Illumination & resources

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Black History Month: A History of Forced Illumination

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In honor of Black History Month, we are starting conversations about racism and bringing awareness to how light pollution impacts the Black community.

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A journey through the bright night Playful learning even if the topic is very sober? Together with my children Benjamin (10) and Viviane (8) have I designed a board game on the impact of light poll…

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Central Texas Girl Scout Dark Skies patch

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Explore more opportunities for learning and earning! Girl Scouts of Central Texas patches are created locally to provide learning and skill-building activities beyond those listed in Girl Scouts’ program-level handbooks. Every Girl Scout grade level has a patch curriculum that can be accomplished as a troop, as a family, or independently.