Composition of Sunlight and of a Number of Ultraviolet Lamps

THE EMISSION characteristics of lamps used for ultraviolet therapy are not generally known by the physicians using them. This knowledge is important because the wavelength of the radiation determines its effect on the skin. The erythemagenic spectrum of sunlight comprises the radiation from about 280 to 320 mμ. Most ultraviolet lamps, however, contain two erythemagenic spectra: that mentioned above, and the ultraviolet radiation between 250 and 280 mμ. If a lamp has a low content of long-wave ultraviolet above 320 mμ, it will have different effects than that with a high output of the same radiation. For these reasons a number of lamps commercially available were examined to determine the approximate proportion and the types of ultraviolet radiation emitted. Material and Methods The instrument used for this purpose was a General Electric ultraviolet meter. It consists of a photocell sensitive to ultraviolet but not to visible light. The meter