Retroreflective photometry for screen efficiency evaluation

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 degrees on either side of the incident beam. Screen samples, 2.54 cm sq, can be oriented through angles of +/-30 degrees to the incident beam and luminances from 1 ft-L to 10,000 f t-L (from about 3.5 cd/m(2) to 35,000 cd/m(2)) 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.