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Direct and Indirect Light.
Every surface in an environment is illuminated by a combination of
'direct light' and 'reflected light'.
The direct light is light energy which comes directly from a light source
or light sources, attenuated only by some interposed media, such as
smoke, fog or dust. The reflected light is light energy which, after
being emitted from a light source, is reflected from one or more
surfaces in the environment, and may then arrive at other surfaces.
When light energy is reflected from a surface it is attenuated by the
'reflectivity' of the surface, as some of the light energy may be
absorbed by the surface, and some may pass through the surface.
The reflectivity of a surface is often defined as its color.