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.

Alveolar-arterial oxygen tension differences in open-chest dogs

The alveolar-arterial oxygen tension difference has been measured in open-chest dogs both with the lung inflated and collapsed after expiration. In dogs with the lung inflated after expiration the tension differences varied with the magnitude of the alveolar ventilation and were similar to those seen in spontaneously breathing dogs and in intact dogs with positive-pressure respiration. Collapse of the lung resulted in an increase of the alveolar-arterial oxygen tension difference and appreciable tension differences were present during the inspiration of 12% and of 8% oxygen. The tension differences measured at three levels of oxygenation could be caused by the presence of different ventilation/perfusion ratios in various parts of the lung.