Screen gain refer to the screen's ability to reflect incident light. Under the condition of constant incident light angle and flux, the ratio of brightness in a certain direction of the screen to brightness in the ideal state is called the brightness coefficient in this direction, and the maximum value is called screen gain. Generally,set the gain of matte white wall as 1. If the screen gain is less than 1, the incident light will be weakened. If the screen gain is greater than 1, more incident light will be reflected or refracted.