"Cousin Ricky" <ric### [at] yahoocom> wrote:
> BTW, from what little i know of these things, fade_power 1 seems to make
> sense for absorption.  (Point light sources, of course, are subject to the
> inverse square law, i.e., fade_power 2.  The formula POV uses isn't quite
> inverse square, but i have a feeling that the Team did it that way to
> compensate for the limited dynamic range of the output.)

It doesn't make a great deal of difference in rendering terms, but the
physically correct version is usually

fade_power 1000

which triggers the use of exp(-x/D). You tend to see more of the fade_colour
with it than with fade_power 1 or 2.

The exponential comes from Beer's law, which holds for simple homogeneous
materials that don't absorb incredibly strongly (like water).

Tom

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