Originally Posted by RapalloAV
How far should you hold the meter away from the screen to get an accurate reading?
It shouldn't matter, unless you are creating a shadow, or the edges of the screen fall within the sensor area.
If you take a flashlight and move it back from the wall, the wall will get 4x darker every time you double the distance.
If you set the flashlight (or projector) in the same spot, the wall will stay the same brightness when you back away from the wall. The reason for that is that the area of the wall is compressing into a smaller angle of your view at the same rate that the brightness falls off. It cancels out.
Angle affects brightness with high gain screens. With perfect diffuse (gain 1.0) screens, the gain shouldn't matter. Actually, with gain 1.0, each point on the surface emits light with a cosine distribution, but as the angle increases, the surface compresses in your view, conveniently canceling out to produce constant brightness from all angles.Edited by rcohen - 9/30/13 at 7:29am