Germicidal lamp

A germicidal lamp (also known as disinfection lamp or sterilizer lamp) is an electric light that produces ultraviolet C (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 protozoans. It can also be used to produce ozone for water disinfection. They are used in ultraviolet germicidal irradiation (UVGI).

There are four common types available:

Low-pressure mercury 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 or vycor 7913 glass. 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.

As with all gas-discharge lamps, low- and high-pressure mercury lamps exhibit negative resistance and require the use of an external ballast to regulate the current flow. The older lamps that resembled an incandescent lamp were often operated in series with an ordinary 40 W incandescent "appliance" lamp; the incandescent lamp acted as the ballast for the germicidal lamp.

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

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