The Effective Gain of a Projection Screen in an Auditorium

A gain screen is a technology used to increase the light levels seen by the audience without increasing the output of the projector. The quoted gain of the screen is the location of the highest gain, which is available at a single location on the screen (the hot spot), and for a limited number of seat locations near the center aisles. However, the perceived brightness of the image on the screen is not solely determined by the peak brightness of the hot spot, nor is the seat in the center of the auditorium the only location with an audience member. The perceived brightness, a subjective quantity, is more closely related to the total amount of light reflecting from the screen to the viewer than to the single hot spot point. Objectively, what we really want to know is the Lumen value at the viewer's location, rather than the foot-Lambert value of a single point on the screen. Measuring the gain of the screen at many locations in the theater is not practical, but fortunately the information to calculate the gain at each seat exists in the screen specification sheets, and the room geometry. Once the screen gain is calculated for each seat in the auditorium, the overall effective screen gain can be determined from their average. A method is demonstrated for calculating this average screen gain and the overall effective room light level. The gain averaged over the screen and over all seats in the auditorium is always lower than the quoted gain of the screen. For 3D systems using silver screens, the average left eye/right eye crosstalk across the screen is negatively impacted by the screen doing an imperfect job of maintaining polarization, especially at the edges of the auditorium. Larger values of crosstalk are coincident with poor performance from both a gain and uniformity standpoint.

Print ISSN

1545-0279

Electronic ISSN

2160-2492

Published

2010-10

Content type

Information

DOI

10.5594/J17316