A photometric procedure using barrier-layer photocells

Abstract

A procedure is described whereby barrier-layer photocells, corrected so as to have a spectral response curve simulating the ICI luminosity curve, are used in the photometry of light sources of various colors and in the determination of the transmission factors of colored filters. The procedure involves a determination of the illumination-response curve of the cell used, a method of avoiding the difficulties incident to cell fatigue, and a means for correcting for the improper spectral sensitivity of the cell. The method of correcting for the difference between the spectral response of the cell used and the ICI luminosity curve embodies essentially the procedure recommended in 1937 by the International Committee of Weights and Measures for the photometry of light sources which differ in color. Results obtained using the recommended procedure are given. CONTENTS Page

An accurate spectrophotometer for measuring the transmittance of solid and liquid materials

“…One year later, Buchmiiller and Konig [12] described and used a two aperture unit. At NBS , Barbrow [14] used a 10 aperture arrangement, while Hardin g [16] and Cordle and Habel! [2S] at NPL described a two aperture system.…”

Emergency vehicle warning devices:

“…In addition, the standard recommended that the warning lights should be unobstructed by any part of the vehicle 10 deg above to 10 deg below the horizontal of the vehicle and from 45 The lamp should be red or amber in color (using one of the test methods of J678) and should flash between 60 and 120 flashes per minute. In addition to the tests from SAE J545, the unit also has to pass extreme temperature tests.…”

A multipurpose photoelectric reflectometer

“…Without a filter, the spectral response of the Photox cell to a source at 2,840oK is roughly similar to that of the average human observer as represented by the standard luminosity function. Although the Photox cell without filter does not provide as satisfactory duplication of the luminosity function as does the GE cell with the green filter, it has been used with success both in the W4VE LENGTH --MI LLI MI CRONS FIGURE 2.-ICI luminosity function times ICI illuminant C compared with (1) spectral response of G E cell times spectral transmission of green filter times spectral energy of 3,100° K, and (2) spectral response of Pho/ox cell times spectral energy of 2,840oK.…”

“…The changes of current from five round GE cells, three Westinghouse Photox cells, three Weston Photronic type 2 cells, and three Electrocells were m easured while the cells were under constant illumina,tion of approximately 2 foot-candles. The circuit used was designed by BUl'brow [2] to measure the current of a barrierlayer photocell in a current-balancing circuit. The results are shown graphically in figure 3.…”