A simple paper sensor featuring smiley and frowny faces drawn in UV-sensitive ink has been produced by researchers in a bid to keep us safe in the sun.

Scientists say the different expressions appear in sequence as UV exposure increases, offering a low-tech way for people to gauge when it is time to cover up.

The team add that they have produced different versions of the wristband for different skin tones – something they say is important given that darker skin can tolerate greater UV exposure before damage occurs, and more exposure is needed to produce vitamin D.

Further, the sensor can respond to varying levels of the different components of UV radiation: while UVA is thought to cause skin ageing and wrinkles, it is mainly UVB that causes sunburn and leads to skin cancer.

“We are always concerned whether we are exposing ourselves too much to the sun, and we might get a skin cancer, cataract, ageing, or other skin diseases. But if we don’t expose ourself enough to the sun we take the risk of being vitamin D deficient,” said Prof Vipul Bansal, lead author of the study from RMIT University in Australia. 

While Bansal noted weather reports often contain a UV index to give a guide to the strength of UV radiation, it does not tell people whether they are within safe levels of exposure at that time, and is based on metrics for fair skin.

Writing in the journal Nature Communications, Bansal and colleagues describe how they sought to tackle the issue by creating a cheap device based on phosphomolybdic acid, or PMA. This substance turns from colourless to blue in the presence of lactic acid and UV radiation.

The team then used this mixture of lactic acid and PMA as an ink to draw four invisible faces on paper, and used transparent sheets of the sort used for overhead projectors to create filters that they put on top of them. This allowed the researchers to tweak the intensity of UV radiation reaching the ink so that the faces changed colour in sequence as exposure to UV radiation rose from 25% to 50%, then 75%, and finally 100% of a “safe” dose.

The team found that the PMA-based ink turns a darker blue colour under UVB than UVA over the same period of time, meaning that the higher the proportion of UVB in the sunlight an individual is exposed to, the quicker the sensor will indicate a 100% dose of UV radiation.

By further adjusting the number of filters for each of the four faces, the team were able to adjust the system to produce different sensors to work for six different skin tones.

Bansal said that while devices were designed using UV light in the laboratory, they are currently being tested in outdoor conditions. The team hope that the sensors will be on the market in a year, costing about a 1AUD (55p) a piece.

Matthew Gass of the British Association of Dermatologists, who was not involved in the research, said said the product does “have the potential to be another tool that helps people avoid excessive sun exposure, but they are not a replacement for actual sun protection in the form of sunscreen, protective clothing, and making use of shade.”

1 - What is represented on the wristband ?
          a) Sensor
          b) Sun
          c) Faces
          d) UV rays

2 - What is the consequence of UVA rays exposure on our skin ?
          a) Sunburn
          b) Skin ageing
          c) Skin cancer
          d) Herpes zoster

3 - What is the ink’s colour without UV exposure ?
          a) Blue
          b) Colour of the skin
          c) Dark
          d) Invisible 

4 - Where the product has been invented ?
          a) Australia
          b) United States of America
          c) China 
          d) England

A stained glass window designed on an iPad by David Hockney to celebrate the Queen's reign has been unveiled at Westminster Abbey, saying:  "I hope she'll like it".

The window, the artist's first work in stained glass, reflects the Queen's love for and connection with the countryside.

Hockney's design was created on his iPad and is set within his beloved Yorkshire and features hawthorn blossom.

It uses his distinct colour palette of yellow, red, blue, pink, orange and greens.

The new window, called The Queen's Window, can be found in the Abbey's north transept.

Hockney was asked to design something symbolic or representational, rather than a figurative design.

Attending the unveiling, Hockney said: "The iPad is back-lit like a window. It's a natural thing to use.

"Landscape is nature. The previous window put up in here was also nature, lilies.

"I chose the hawthorn which is [for] four days [like] the moment when champagne looks as though it's been poured over all the bushes.

"It's a rather celebratory thing. It's the height of the spring and summer".

The artist said of the window's Westminster Abbey home: "I know this is a historic place and I know it's going to last."

Hockney once said that he turned down the chance to paint the Queen because he was "very busy painting England actually, her country".

He said of designing his first stained glass window: "I learnt something about glass. It was a challenge."

The artist said of Westminster Abbey: "I know this is a historic place and I know it's going to last."

Asked whether he had any response to the window from the Queen, who has seen a sketch and will see the real thing when she visits Westminster Abbey in November, said: "Not yet, but I hope she'll like it. I'm sure she will.” he said: "Not yet but I hope she'll like it. I'm sure she will."

Westminster Abbey said that the result "reflects the Queen as a countrywoman and her widespread delight in, and yearning for, the countryside".

The Dean of Westminster, the Very Reverend Dr John Hall, said: "I'm excited by it.

"I think there's absolutely no harm at all in having something which is particular and vibrant and different.

"Some of the glass here is not very good. Some of it is not too bad, but this has a wonderful, beautiful, easily accessible vibrant colour. I think people will enjoy it."

He added: "It's going to be here until the end. Who knows what's going to happen in the future."

Hockney, 81, is one of Britain's most-loved artists and famous for his Yorkshire landscapes and paintings of Californian life.

Barley Studio, a stained glass studio based in York, created the window using traditional techniques.

Sometimes an airport is just a strip of asphalt on a flat bit of land outside of town. Other times, as with India's new Pakyong Airport, it's a breathtaking piece of engineering on the roof of the world.

Set in the Himalayan mountains at a height of over 1,400 meters (4,593 feet), the facility serving a remote area of Sikkim state offers one of the most dramatic airport approaches on the planet.

Its inauguration on Monday also marked a milestone for aviation and travel in India.

"After the opening of the airport there are now 100 operational airports in India." said Narendra Modi, India's prime minister, during a speech at Pakyong's opening ceremony on Monday.

"This airport was built at a cost of $68.7 million and showcases our engineers, workers and their potential -- how the mountains were cleared, the ditch was filled, the heavy rains they dealt with. This is truly an amazing feat of engineering."

As part of that work, an 80.38 meter embankment was built to make space for the 1.7-kilometer-long and 30-meter-wide runway, which is enclosed by deep valleys.

The airport's 2,380-square-meter terminal can accommodate up to 100 passengers.

But its real asset is the incredible Himalayan scenery -- a widescreen landscape captured in a series of stunning images by Indian photographer Rajiv Srivastava, who runs the website Imazin India.

The airport will enter commercial passenger service when SpiceJet, one of the country's largest low-cost airlines launches two daily routes to Pakyong Airport (Pakyong-Kolkata and Pakyong-Guwahati) from October 4.

The Pakyong-Kolkata flight will take around 1.5 hours and the Pakyong-Guwahati route will take slightly longer than an hour.

The flights will offer some much-needed accessibility to the region. Before the opening of Pakyong, the nearest airport to Sikkim's state capital of Gangtok was Bagdogra, in West Bengal -- a five-hour drive.

Pakyong Airport is only 30 kilometers south of Gangtok.

It's hoped that the new airport will boost tourism in the region.

Bordered by Bhutan and Nepal, the northeastern state is known for its scenic Himalayan landscapes, boasting 28 mountain peaks, 21 glaciers and more than 200 lakes.

"Sikkim is the beloved destination of tourists," said Modi during the inauguration ceremony.

"Once the airport becomes operational, the number of tourists is going to go up. The new airport will also provide employment for the youth and in turn, hotels, guest houses, restaurants, tour guides and so on."