A daily record of ultraviolet solar and sky radiation in Washington, 1941 to 1943

A descript ion is given of a photoelectric ultraviolet-intensity meter and automatic integrating and recordin g apparatus for measuring the biologically effective component of ultraviolet radiation, of wavelengths 3132 A and shorter, from the sun and the entire sky, incident on a horizontal plane, under various meteorological conditions. Methods of standardization, in absolute value, are described (see RP1542 for supplementary data). A continuous graphical r ecord of the in tegrated daily total amount of biologically effective ultraviolet solar and sky radiation observed during a period of 3 years (1941 to 1943) in Washington, D. C. is given . The monthly totals of biologically effective ultraviolet, in absolute value (milliwatt minutes per square centimeter) mw min/cm2 are also given graphically. On the clearest days the biologically effective component of ultraviolet radiation of wavelengths 3132 A and shorter, incident from the sun and the whole sky at midday, ranges from about 180 microwatts per square centimeter, (p.w/cm 2 ) in midsummer to about 30 /Lw/cm 2 in midwinter. A series of erythema tests is given, correlating the physical (radiometric) measurements with the physiological reaction of the untanned skin, which information is of interest in helotherapy and bioclimatology.