A Method for Automatically Plotting Spectral Energy Distribution of Luminescent Materials

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Abstract
A method is described for measuring automatically the spectral energy distribution of luminescent materials or of other light sources. A photo-multiplier operated on d.c. is used with a standard constant deviation spectrometer for measuring the energy in the spectrum. A compensator has been built in the spectrometer so that the output of the photo-cell is proportional to incident energy of any wave-length. A drive mechanism sweeps the spectrum across the exit slit at constant wave-length rate, and the photo-cell output appears on the chart of a standard photoelectric recorder. Errors, due chiefly to inaccuracies in milling the compensator, are less than 5 percent except in the extreme violet. Curves repeat within 1 or 2 percent. Spectral curves can be taken of surfaces whose brightness is as low as 1 foot lambert. The time to obtain a distribution curve may be varied from one-half to two minutes by a change of gears.
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