Gain (projection screens)
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Gain is a property of a projection screen, defined by how much brightness is visible from the screen's centre when the viewer is looking at that point on-axis to the centre. Gain is controlled by diffusion of the screen, and governs the degree which light from the projector is scattered.
[edit] Further Meaning
A gain of 1.0 means the amount of light that is projected on the screen returns to the viewer at the same brightness: none is absorbed and all is re-radiated with perfect uniformity from all viewing angles. If one was to isolate certain rays striking the screen, he/she would see the rays diffuse to form a perfect hemisphere shape. A block of magnesium carbonate (MgCO3) or a matte white screen will result in a gain of 1.0.
But as gain increases, the shape of the hemisphere and hence the uniformity is affected. With increasing gain, the hemisphere radius would decrease along the surface of the screen, and the radius protruding perpendicular from screen will lengthen. The centre of the screen will become brighter and the edges of the screen will dim so uniformity decreases.
