Sunlamp

(electricity) A mercury-vapor gas-discharge tube used to produce ultraviolet radiation for therapeutic or cosmetic purposes.

A special form of mercury arc discharge lamp designed to produce ultraviolet radiation. These lamps also produce some radiant energy in the visible region of the spectrum, thus having a light output as well as an ultraviolet output. The lamps are principally used for producing a skin tan on the human body. The less common uses include therapeutically producing vitamin D in the body for the treatment of rickets and causing fluorescence or photochemical reactions.

Sunlamps have ultraviolet radiation at wavelengths above 280 nanometers. The lower limit is set by the fact that the quartz and high-silica glass used for lamp envelopes do not transmit below 280 nm. The two lamps designed for tanning are the FS-40 and the RS. The FS-40 tubular fluorescent lamp ( illus. a) operates with a low-pressure mercury arc that causes a special chemical phosphor coating inside the tube to radiate ultraviolet energy. The RS sunlamp ( illus. b) is a reflector unit containing a high-pressure mercury arc tube for generating ultraviolet energy plus a tungsten filament (similar to incandescent lamp filaments) in series with the arc tube to serve as a ballast. See also Mercury-vapor lamp; Ultraviolet lamp.

Structure of sunlamps. (a) FS-40. (b) RS.