||In the earliest days of artificial sun-tanning it was customary to employ a simple carbon arc as the source of ultra-violet radiation. To enhance the UV output special carbons were produced which had cores of other materials emitting the shorter wavelengths. Typically, the arc was ballasted by a coil of nichrome resistance wire which became heated and contributed long wave infra-red to give a mild heating effect.
Of course, the bare quartz mercury arc tube superseded the carbon arc as soon as it became available in the late 1930's and it removed the continuous need to adjust the arc as the carbons burned away. However much shorter wavelengths were produced and it was very easy to receive an over-dose of UV leading to serious skin burn.
It was not until the late 1940's that a reliable sun-tanning system was perfected, with Osram's development of the Ultra-Vitalux lamp shown here. It employs an 80-watt quartz mercury arc tube and tungsten ballast filament all within the same outer bulb. The filament also contributes to the short-wave infra red-part of the spectrum to produce a heating effect of the skin which was believed to have other therapeutic benefits. The outer bulb is fabricated in special glass which transmits the medium wave ultra violet only, excluding the very short wavelength rays which cause more rapid skin burning. The precise composition of the glass is unknown, but in these earliest lamps it is based on a soft glass and has a greyish-pink colouration. To reduce the overall size of the sun-tanning equipment, a reflector lamp of the same style was introduced soon after this round version. The design was copied by Philips in its MLU lamp, and adopted by GE as its RS Sunlamp a few years later.