For ideal diffuse source (POV 3.5):

  fade_power 2 fade_distance sqrt(area-of-emitting-surface)
  spotlight radius -90 falloff 90 tightness 1

Dividing the source to multiple smaller sources improves
the intensity simulation for objects close to to the source.
Same applies when the shape of the source differs much from
circle or square.

When the source is not diffuse but directs light like a spot light
fade_distance should be increased. The modifier depends on the
spotlight parameters. For spotlight radius 0 falloff FO tightness 0
my guess for the modifier would be 90^2/FO^2, until I find
out how lighting engineers calculate spotlights.


_____________
Kari Kivisalo

Post a reply to this message