POV-Ray : Newsgroups : povray.general : Light Attenuation : Re: Light Attenuation Server Time
21 Apr 2024 03:34:42 EDT (-0400)
  Re: Light Attenuation  
From: Alain
Date: 10 Mar 2011 13:02:34
Message: <4d79123a@news.povray.org>

> 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
>
>

For materials, the atenuation is the result of the interaction of the 
light with the material. Atenuation is caused by absorbtion.

For the light's atenuation over a distance, you need to use the inverse 
square rule to get realistic atenuation, and absolutely need to use 
fade_power 2. It's the spreading of the light's energy that causes the 
atenuation.
There is NO absorbtion in this case. As there is no absorbtion, any 
formula based on absorbtion would be totaly unrealistic.

The terms are the same, but the physical reality modeled is not.



Alain


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