A germicidal lamp is a special type of Ultraviolet light (UVC). UV light bulbs produce short-wave ultraviolet light, that prevents the DNA from 'unzipping', thus stopping multiplication. Use of a Germicidal lamp will lead to the death of bacteria on exposed surfaces. They can also be used for water disinfection and purification.
They come in two main types Low pressure lamps and Medium pressure lamps. Low pressure lamps are similar to Fluorescent lamps, with a wavelength of 253.7nm. The most common Germicidal lamp looks just like a fluorescent tube but with changes to the glass and the lack of fluorescent phosphor means the 253.7nm ultraviolet light passes through unmodified unlike fluorescents that produce visible light. (note germicidal tubes still produce a small amount of light)
Medium pressure lamps are similar to HID lamps. They produce a broad-band UV-C radiation. These are used for industrial water treatment because they are intense radiation source. They produce a very bright bluish white light light.
Germicidal lamps are used to sterilise work tops, tools and other surfaces. They are also used for water sterilisation.