Originally Posted by rotelmania
So the calorimeter does not need to be placed right up against the screen?
With a front projector setup, the screen is reflecting the light from the projector back to the viewing area. This is different than most television displays (either flat panel or rear projection) where the light source is behind
the screen. As angryht notes, you can either measure the light source directly, or the reflections off the screen. You can't measure the screen itself directly.