Light attenuation is used to model the decrease in light intensity as the light travels through a transparent
object. The keywords
fade_color are specified in
fade_distance value determines the distance the light has to travel to reach half intensity while
fade_power value determines how fast the light will fall off.
fade_color colorizes the
attenuation. For realistic effects a fade power of 1 to 2 should be used. Default values for
fade_distance is 0.0 which turns this feature off. Default for
<1,1,1> there is no attenuation. The actual colors give colored
<1,0,0> looks red, not cyan as in media.
The attenuation is calculated by a formula similar to that used for light source attenuation.
If you set fade_power in the interior of an object at 1000 or above, a realistic exponential attenuation function
will be used:
Attenuation = exp(-depth/fade_dist)
fade_distance keywords were originally specified in
but are now properly specified in
interior. They are accepted in
finish for backward
compatibility and generate a warning message.