Gain is a measurement of the reflectivity of any screen or projection surface. The gain 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. Therefore, a screen with a gain of 1.0 will reflect the same amount of light as that from a white board. A screen rated at 1.5 gain will reflect 50% more light as that from a white board. A gray screen with a 0.8 rating will reflect 80% of the light from a white board.
Gain standards are certified and used to base line measurements of gain in screen surfaces. The yield of reflected light from an illuminated gain standard is defined to have value of 1.0. Any surface under test is compared to the performance of the light on the gain standard and a logarithmic measurement is furnished via a light meter. This measurement is expressed as a multiple of 1 or as a fraction of one, which is a number between 1.0 and zero.
There are no negative gain screens in existence. The numbers between 1.0 and zero are positive numbers. Screens with gain below 1.0 are more accurately characterized as fractional gain screens.
Screen gain can be manipulated and controlled to direct light in a specific distribution or to reject light from specific angular zones. Gain can also be reduced via a selection of pigments and use of dyes to tint the surface away from white towards gray values with the goal of improving black level performance and enhancing contrast.