All screen and projection products have their gain factor which can either be high or low. Many white home theater screens are low gain and carry ratings from 1.0 to 1.3, while some gray screens are rated as low as 0.8 gain. These numbers would actually mean nothing to people who have not gone shopping for a screen before.
Gain is a term that refers to the measurement of the reflectivity of any screen or projection surface. The number represents a ratio of the light that is reflected from the screen as compared to the light reflected from a standard white magnesium oxide board. It is measured from the point where the screen is at its brightest which is often referred to as the Peak Gain at Zero Degrees Viewing Axis. On the other hand, the Half Gain Viewing Angle is the angle at which the gain reading drops to 50% of the Peak Value.