Type drop-down list
Sets the type of decay to use. There are three types to choose from.
None (The default.) Applies no decay. The light maintains full strength from its source to infinity, unless you turn on far attenuation.
Inverse Applies inverse decay. The formula is luminance=R 0 /R, where R0 is the radial source of the light if no attenuation is used, or the Near End value of the light if attenuation is used. R is the radial distance of the illuminated surface from R0.
Inverse Square Applies inverse-square decay. The formula for this is (R 0 /R) 2 . This is actually the "real-world" decay of light, but you might find it too dim in the world of computer graphics.