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The illusory brightness difference seen between the squares in the preceding figure is an example of simultaneous lightness contrast. A contrast effect refers to perceiving a difference between stimuli that is greater than any difference in actual intensity. Lightness contrast is often used in painting to depict light and to give particular emphasis to a feature or area in the painting. This is achieved by painting some region(s) of the painting in very dark colours and then using very light colours for adjacent areas or features. In art, the technical term for this technique is chiaroscuro, an Italian term referring to the interplay of light and dark with the goal of intensifying the feeling or mood in a work of art.

The "invention" of chiaroscuro is often attributed to the Italian renaissance painter Caravaggio. Caravaggio was seen as a rebellious painter who often defied traditional rules. Whereas some painters would place their art in areas with specific lighting to accentuate certain features, Caravaggio set out to reproduce this effect in the paintings themselves.

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http://www.archlighting.com/projects/controlling-glare_o

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Good lighting design practice either diffuses the light to reduce the luminance or shields the source from view. The control of glare in electric lighting is generally called shielding. For natural light, however, the term shading is used. While technically they are almost the same thing, the slight difference in language is welcome to help differentiate between lighting and daylighting.

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At present, the Illuminating Engineering Society (IES) defines glare as one of two conditions:

Too much light

Excessive contrast, meaning the range of luminance in the field of view is too great

In practice, glare is almost always a situation where a source of unshielded light is at least 1,000 times brighter than the average visual field. For instance, since the night sky is dark, almost all outdoor light sources, such as a street luminaire or automobile headlight, cause glare. To evaluate glare, however, light can't be measured in lux or footcandles—one must use luminance, which typically is measured in candelas per square meter (cd/m2) or nits. It also is common, although not technically correct, to use the term brightness rather than luminance.

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the intensity of light emitted from a surface per unit area in a given direction.

the component of a television signal that carries information on the brightness of the image.

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Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target