Quote - Maybe you would like to try and experiment with that Paolo :) I tried your way, also tried converting the plane which serves as the screen to light with a texture, and still no reflections bouncing off the surrounding walls. Must the surrounding walls also be almost pure white?

 

Are your walls matte? (Obviously, the screen is going to light the room up no matter what with GI.) Are you after the effect shown in this image?

 

 

That's actually a specular highlight, or a blurred reflection. (they're the same thing in Lux [and real life]). The disadvantage of the matte material is you don't get these, you get the result on the left. You need to use a pretty rough glossy material, with a specular color of maybe 50 or so. (That would be equal to an IOR of about 1.45-1.5).

 

Btw, that image came from this thread on CGTalk, which should be required reading for operating an unbiased renderer. ;) http://forums.cgsociety.org/showthread.php?f=21&t=650761f=21&t=650761