47] Lighting strategies for Imagine, By Gregory Denby.

The program's light simulation only slightly resembles that found in nature. The amount of light seen on a surface is controlled by the light's angle of incidence. The intensity of the light may fall off in inverse proportion to the distance, if You exclude an initial sphere of maximum intensity. However, the light is not reflected by surfaces, or scattered by an atmosphere. As a result, the generally diffuse appearance of light in every day experience is not directly available. Fortunately, there are a number of ways to approximate natural illumination.

The following techniques make an assumption common to usual methods of naturalistic representation. If an image is consistent in its construction, and does not obviously diverge from usual perceptions, the viewer will tend to assume the image is "real". A simple instance of this occurs in paintings.
Artist's colors did not achieve a full spectrum until near the beginning of the 20th century. And even after that, few artists ever work with more than a few hundred hues. Nevertheless, images whose range of colors generally fit ordinary experience are perceived as being "real", despite lacking the subtlety really existing. In like manner, the lighting methods presented here attempt to give approximations of genuine light that will give an semblance of reality.

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