ULTRAVIOLET-INCANDESCENT-LAMPS
An incandescent lamp consisted of a metal wire in a
glass bulb without oxygen. An electric current heated
the metal wire and made it glow white-hot while the
lack of oxygen prevented the wire from burning.
Apart from light, incandescent lamps produced a lot
of infrared- and a small amount of ultraviolet
radiation. Raising the temperature of the filament of
an incandescent lamp well above the regular 2500
degrees Celsius increased the production of
ultraviolet radiation but the ultraviolet yield would still
never be more than a few tenths of a percent.
Sunlamps based on conventional incandescent
lamps never became successful therefore with one
possible exception. The Philips Zonlicht lamp,
introduced in 1918, was an incandescent lamp with
a spectral distribution that resembled that of natural
sunlight. This lamp was intended to be used for the
illumination of stores and warehouses however and not for medical purposes. A
sunlamp that looked like an incandescent lamp most often turned out to be a mercury
vapour arc discharge lamp protected by an additional outer bulb or it was a blended
lamp, i.e., a mercury vapour arc discharge lamp, ballasted with a filament in the same
bulb.
