Jaime Vives Piqueres wrote:
>
>   Hmmm... regardless of the light intensity or the scene scale? I'm not
> sure there is a value or fomula that can be seen as "definive".

There is but it's not sqrt(area), it's sqrt(sqrt(area)) or sqrt(diameter)
in case of square source. I calculated this some time ago but mixed
variables :)

fade_distance is the only way to specify the physical dimension of the
source for intensity calculations. I integrated in matlab 2601 point sources
over a 25x25 square and calculated the relative error to fade_distance 1
and fade_distance 5. It turned out that fade_distance sqrt(sqrt(area))
best matches the integrated axial intensity. Division by sqrt(area)
normalises the equation so it can be compared.

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

In far field (5xdiameter) all the formulas converge to 1/d^2 unless
fade_distance is really big or small compared to source dimensions.


_____________
Kari Kivisalo

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