Kari Kivisalo wrote:
> Jaime Vives Piqueres wrote:
>>     color LightColor*7*pow((DX+DZ)/2,2)
>>     fade_distance 1
>> 
>>   and you will see they give the same scene!'
> 
> Now scale the whole scene by 0.00001 and keep fade_distance 1 :)
> Use one source.

  Hmmm... now I see it!  I used a variable to scale down the entire scene 
at will (including light color), and tested both methods. I found that 
"fade_distance 1" and "sqrt(sqrt(area))" give the same results for anything 
above 1, and both are constant (they give the same light at any scale above 
1). For scales smaller than fade_distance, both start to give wrong 
results: with "fade_distance 1"  light loses more and more intensity, while 
"sqrt(sqrt(area))" behaves the contrary, but not so hardly. 

  Then, can this means the POV attenuation formula is not really 
appropriated for values bellow 1? Anyhow, as I assumed a scale of 1 unit = 
1 cm for my macro, this not really important: any of both methods works 
fine. 

  But  in the meanwhile, I found that srqt(sqrt(area)) permits a more 
intuitive use of my MAX_LUMENS variable, so I will use it with your 
permision. :)

> The equation used in pov clearly tries to estimate the combined axial near
> field of multiple point sources on planar surface. fade_distance tells the
> size of the source.

  Hmmm... then this is why it is different from the typical inverse square 
law for point sources? This will be very helpful on the official docs. The 
current explanation is somewhat "difficult to understand" for mere mortals.

  Thanks for your explanations, Kari: fade_distance was the more intriguing 
part of light_sources for me.

-- 
Jaime Vives Piqueres

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

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