Gain (projection screens)
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.
Gain is measured from the vantage point where the screen is at its brightest, which is directly in front and perpendicular to the screen. Technically the measurement of gain at this point is known as Peak Gain at Zero Degrees Viewing Axis. If you move to the side and view the screen at an angle the brightness of the projected image drops. The angle at which the gain reading drops to 50% of the peak value is known as the Half Gain Viewing Angle. A person viewing the screen from this angle will see an image half as bright as the person seated at the center position.
