Light attenuation is used to model the decrease in light intensity as the light travels through a transparent object. The keywords fade_power Fade_Power and fade_distance Fade_Distance keywords are specified in the interior statement.
The fade_distance value determines the distance the light has to travel to reach half intensity while the fade_power value determines how fast the light will fall off. For realistic effects a fade power of 1 to 2 should be used. Default values for both keywords is 0.0 which turns this feature off.
The attenuation is calculated by a formula similar to that used for light source attenuation.
The fade_power and fade_distance keywords were original specified in finish but are now properly specified in interior. They are accepted in finish for backward compatibility and generate a warning message.