Kari Kivisalo wrote:

>There is but it's not sqrt(area), it's sqrt(sqrt(area)) or sqrt(diameter)
>in case of square source. 
> fade_distance is the only way to specify the physical dimension of the
> source for intensity calculations. 

  I insist: for which light color? Because it all depends on the color you 
give to the light_source.When I read the definition of fade_distance from 
the POV  manual, I deduce it can be done equally with the color. Then, take 
for example your cornell box scene, and change these light source values:

    color LightColor*7
    fade_distance (DX+DZ)/2

  with these other:

    color LightColor*7*pow((DX+DZ)/2,2)
    fade_distance 1

  and you will see they give the same scene! So, what this means?

> http://www.pp.htv.fi/kkivisal/relative_error.gif

  Sorry, I'm not that mathematically minded: I do not see what the graphic 
is suposed to show... :( I really prefer to test things with pov! :)

-- 
Jaime Vives Piqueres

La Persistencia de la Ignorancia
http://www.ignorancia.org

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