Retroreflective Photometry for Screen Efficiency Evaluation

Abstract

An analytical treatment is given which shows that the peak luminance gain and lobe width of a back or front projection screen material can be used as coordinates on a graph to determine the transmission or reflection efficiency. The analysis assumes that the angular distribution of the gain can be expressed as a power of a cosine function. Also, a screen photometer is described which is based upon the adaptation of a spectrometer to measure screens having retroreflective characteristics. The photometer is capable of measuring luminance on the retroreflective axis and out to 15° on either side of the incident beam. Screen samples, 2.54 cm sq, can be oriented through angles of ±30° to the incident beam and luminances from 1 ft-L to 10,000 ft-L (from about 3.5 cd/m² to 35,000 cd/m²) can be handled. The instrument has three modes of operation: visual, photoelectric, and photographic. A graph is presented illustrating the application of the analytical technique to provide a rapid performance evaluation and comparison of screen efficiencies.

© 1970 Optical Society of America