A Photoelectric Cell for Measuring Ultraviolet Solar and Sky Radiation on a Horizontal Plane1

Measurements of ultraviolet solar radiation in Washington, 1936 to 1942

“…This was repeatedly observed in the measurements of 1942 ( fig. 10), the most of which were made in connection with the calibration of a photoelectric cell used for measuring ultraviolet solar and sky radiation incident on a horizontal plane (4,11]. In the course of these measurements of solar and sky radiation it was repeatedly observed (by shadowing the receiver from the direct solar rays) that it was only during the noon hours of the clearest days in early summer that the ultraviolet radiation from the whole sky incident on a horizontal surface was slightly less than the directly incident solar rays, and that when the sky was slightly turbid, the ultraviolet radiation from the whole sky was at least 2.5 times greater than the directly incident solar rays [3,4].…”

“…In the meantime, it has been established that the spectral range of the tanning reaction extends to longer wavelengths (9), upon which basis it seemed logical to place the limit of biological effectiveness at 3200 A [10]. Another reason for considering the adoption of a threshold of biological effectiveness at longer wavelengths was the development of photocells sensitive only to wavelengths shorter than about 3200 A, for use in measuring solar and sky radiation on a horizontal plane [11]. If reproducible photoelectric cells with the same threshold of response were available, ultraviolet radiometry would be greatly simplified.…”

“…(b) to secure data required in working out methods of evaluating the biologically effective component of ultraviolet solar radiation [I)-required particularly in one method of standardizing ultraviolet dosage-intensity meters [4,11]; and (c) to determine whether, with the accuracy attainable in the radiometric measurements, the reduction factors (F, G) used in the calculations of ultraviolet intensities, will require modifications with changes in the spectral quality of the biologically effective ultraviolet radiation, which varies with the ozone concentration in the stratosphere, which, in turn, varies with the latitude, the season, the barometric pressure (movements of masses of polar air) and, less systematically, with the sunspot cycle [5,6,18].…”

Measurements of ultraviolet solar- and sky-radiation intensities in high latitudes

“…By installing simple automatic measuring and recording apparatus [2,3], for the first t ime a cont inuous record was obtained, in absolute value, of the intensity of the biologically effective ultraviolet radiation from the sun and from the entire sky incident on a horizont al plane, under various meteorological conditions, in the polar regions . The information thus obtained is novel and is of considerable biological interest, particularly to t he medical profession.…”

“…2 1 Numbers in brackets indicate the literature references and notes at the end of this paper. 2 Acknowledgment is made to the Council on Physical Therapy of the American Medical Association for two grants i n aid to develop tbis type of ultraviolet meter [2) for use in beliotherapy. In an u nforeseen manner the first practical application of these instruments has been to the securing of quantitative data on ultraviolet intensities in the polar regions.…”