For POV, light attenuation uses the function a=2/(1+(d/FD)^FP) [3.4.7.9] for
light sources.  However for materials, the light attenuation function is
similar: a=1/(1+(d/FD)^FP), but it also allows you to implement a realistic
exponential function: a=exp(-d/FD) by setting FP=>1000.  My general question, is
why has this more realistic function (generally following Lambert Law of
Absorption) not been implemented for light sources as well?  By playing with the
FD & FP values, a close approximation can be found for some range (the best
seems to be by using FP=exp(1)=2.72) however it is limited to a specific range
and not the whole distance (e.g an absolute deviation of ~+/-0.006 exists only
from a relative distance of about 1.74 on, for a pecentage deviation it is even
more limited, for a +/-10% deviation from ~1.51 to ~3.67)

-tgq

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