Well, i had this problem someday, but i haven''t the answer yet. I think that what wolf mean, and i would like to do, is for example:

if you look inside a abandoned house''s room, full of dust(powder, sorry, my english isn''t that well). So the window is almost full opened, and you see the sun''s beamenter in and make a glow, similar to the lamp. Or even a lantern. You guys know what i mean. I searched for it, and found raytracin, but... the problem proceeds...

"There are people who live in the reality. We recreate it!"