Germicidal lamp

A germicidal lamp is a special type of lamp which produces ultraviolet (UVC) light. This short-wave ultraviolet light disrupts DNA base pairing causing formation of pyrimidine dimers and leads to the inactivation of bacteria, viruses, and protozoa. It can also be used to produce ozone for water disinfection.

There are three common types available:

Low-pressure lamps are very similar to a fluorescent lamp, with a wavelength of 253.7 nm (1182.5 THz).

The most common form of germicidal lamp looks similar to an ordinary fluorescent lamp but the tube contains no fluorescent phosphor. In addition, rather than being made of ordinary borosilicate glass, the tube is made of fused quartz. These two changes combine to allow the 253.7 nm ultraviolet light produced by the mercury arc to pass out of the lamp unmodified (whereas, in common fluorescent lamps, it causes the phosphor to fluoresce, producing visible light). Germicidal lamps still produce a small amount of visible light due to other mercury radiation bands.

An older design looks like an incandescent lamp but with the envelope containing a few droplets of mercury. In this design, the incandescent filament heats the mercury, producing a vapor which eventually allows an arc to be struck, short circuiting the incandescent filament.

At the last two decades the rapid development is acquired so-called excimer lamps having a number of advantages over the other sources of ultraviolet and even vacuum ultraviolet radiation.

High-pressure lamps are much more similar to HID lamps than fluorescent lamps.

These lamps radiate a broad-band UV-C radiation, rather than a single line. They are widely used in industrial water treatment, because they are very intense radiation sources. They are as efficient as low-pressure lamps. High-pressure lamps produce very bright bluish white light.

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