Problems with polygonal light source

I'm trying to create a rectangular light positioned on the ceiling of a room so
I use
void light bright
0
0
3 100 100 100

bright polygon rectangular_light
0
0
12 2.25 0.05 2
  2.25 0.05 3
  2.75 0.05 3
  2.75 0.05 2

but I have to position the light just below the ceiling (at height 0) so that
it's not obstructed by it and also the light only radiates from the bottom of
it's polygonal shape leaving the ceiling completely black. Can anyone advise me
what to do?

Thanks

Tarik

···

--
Tarik Rahman
PhD student, Institue of Perception, Action and Behaviour
School of Informatics
University of Edinburgh

Hi Tarik,

For a downward-directed light source, the ceiling is illuminated by interreflected light, which is approximated (to zeroeth order) with the -av setting in Radiance. Better approximations may be obtained by setting -ab to 1 or greater.

-Greg

···

From: Tarik Rahman <[email protected]>
Date: January 11, 2005 9:43:06 AM PST

I'm trying to create a rectangular light positioned on the ceiling of a room so
I use
void light bright
0
3 100 100 100

bright polygon rectangular_light
0
12 2.25 0.05 2
  2.25 0.05 3
  2.75 0.05 3
  2.75 0.05 2

but I have to position the light just below the ceiling (at height 0) so that
it's not obstructed by it and also the light only radiates from the bottom of
it's polygonal shape leaving the ceiling completely black. Can anyone advise me
what to do?

Thanks

Tarik