High-Brightness Projection Screens with High Ambient Light Rejection

Efforts to produce brighter projected pictures have in general been confined to improving projector lamps, illuminating systems and projection lenses. The role of the projection screen in the total projection system is equally important. A careful analysis of the photometric characteristics of conventional front-projection screen materials has been made and it has been found that they are generally unsatisfactory for use in ambient light, and inefficient in their utilization of image light. Calculations have been made of theoretically ideal luminance (brightness) gains possible as a function of the spread angle needed to accommodate any given audience space. The interplay of luminance gain, screen material, spread angle and ambient light rejection is discussed. — A new screen material having characteristics close to the theoretically ideal has been developed. The necessity of curving the screen with this material for the most effective utilization of image light and rejection of ambient light is explained and analyzed in depth. A practical screen has been produced using this new material, with appropriate curvature, which has proved to be approximately six times brighter than the best existing screens with excellent performance in high ambient light. It is emphasized that this increased brightness allows expanded use of small-format films, stereo projection and low-wattage projectors, and opens the way for other novel applications.