Stray light elimination in making projection display measurements

Electronic front-projection display specifications are often based on measurements made in ideal darkroom conditions. However, not everyone has access to such a facility. In many environments, ambient light from other sources in the room illuminates the screen. This includes room lights directly illuminating the screen and the reflection of these light sources off of walls, floors, furniture, and other objects. Additionally, back-reflections from the projection screen must be considered. These stray light components contribute to the measured value, giving an inaccurate measurement of the projector light output. Thus, these conditions may make the task of adequately comparing and evaluating different projection systems difficult. We can better verify whether the projector is operating according to its specifications or compare its performance with other projectors by compensating for stray light. A simple projection mask constructed from black plastic and a stray-light elimination tube are presented as solutions that can provide an accurate measurement of projector light output in many ambient light conditions.