By default POV-Ray does not diminish light from any light source as it travels through space. In order to get a
more realistic effect
fade_power keywords followed by float values can be
used to model the distance based falloff in light intensity.
is used to specify the distance at which the full light intensity arrives, i. e. the intensity which was given by the COLOR
specification. The actual attenuation is described by the
which determines the falloff rate. For example linear or quadratic falloff can be used by setting
to 1 or 2 respectively. The complete formula to calculate the factor by which the light is attenuated is
d being the distance the light has traveled.
You should note two important facts: First, for
Fade_Distance larger than one the light
intensity at distances smaller than
Fade_Distance actually increases. This is necessary to get
the light source color if the distance traveled equals the
Fade_Distance. Second, only light
coming directly from light sources is attenuated. Reflected or refracted light is not attenuated by distance.