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Agermicidal lamp (also known asdisinfection lamp orsterilizer lamp) is anelectric light that producesultraviolet C (UVC) light. This short-wave ultraviolet light disruptsDNAbase pairing, causing formation ofpyrimidine dimers, and leads to the inactivation ofbacteria,viruses, andprotozoans. It can also be used to produceozone forwater disinfection. They are used inultraviolet germicidal irradiation (UVGI).
There are four common types available:
Low-pressure mercury lamps are very similar to afluorescent lamp, with awavelength 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 fluorescentphosphor. In addition, rather than being made of ordinaryborosilicate glass, the tube is made offused quartz orvycor 7913[1] glass. These two changes combine to allow the 253.7 nm ultraviolet light produced by themercury arc to pass out of the lamp unmodified (whereas, in common fluorescent lamps, it causes the phosphor tofluoresce, producingvisible light). Germicidal lamps still produce a small amount of visible light due to other mercury radiation bands.
An older design looks like anincandescent 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 allgas-discharge lamps, low- and high-pressure mercury lamps exhibitnegative resistance and require the use of an externalballast 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 toHID 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.
Excimer lamps emit narrow-band UVC andvacuum-ultraviolet radiation at a variety of wavelengths depending on the medium. They are mercury-free and reach full output quicker than a mercury lamp, and generate less heat. Excimer emission at 207 and 222 nm appears to be safer than traditional 254 nm germicidal radiation, due to greatly reduced penetration of these wavelengths in human skin.
Recent developments inlight-emitting diode (LED) technology have led to the commercial availability of UVC LED sources.
UVC LEDs use semiconductor materials to produce light in a solid-state device. The wavelength of emission is tuneable by adjusting the chemistry of the semiconductor material, giving a selectivity to the emission profile of the LED across, and beyond, the germicidal wavelength band. Advances in understanding and synthesis of theAlGaN materials system led to significant increases in the output power, device lifetime, and efficiency of UVC LEDs in the early 2010s.
The reduced size of LEDs opens up options for small reactor systems allowing point-of-use applications and integration into medical devices.[2] Low power consumption of semiconductors introduce UV disinfection systems that utilized small solar cells in remote or Third World applications.[2]
By 2019, LEDs made up 41.4% of UV light sales, up from 19.2% in 2014[3] The UV-C LED global market is expected to rise from $223m in 2017 to US$991m in 2023.[4]
Germicidal lamps are used to sterilize workspaces and tools used in biology laboratories and medical facilities. If the quartz envelope transmits shorter wavelengths, such as the 185 nm mercury emission line, they can also be used whereverozone is desired, for example, in the sanitizing systems ofhot tubs andaquariums. They are also used bygeologists to provoke fluorescence inmineral samples, aiding in their identification. In this application, the light produced by the lamp is usuallyfiltered to remove as much visible light as possible, leaving just the UV light. Germicidal lamps are also used in waste water treatment in order to kill microorganisms.
The light produced by germicidal lamps is also used to eraseEPROMs; the ultraviolet photons are sufficiently energetic to allow the electrons trapped on thetransistors'floating gates to tunnel through the gate insulation, eventually removing the stored charge that represents binary ones and zeroes.
For most purposes, ozone production would be a detrimental side effect of lamp operation. To prevent this, most germicidal lamps are treated to absorb the 185 nm mercury emission line (which is the longest wavelength of mercury light which will ionize oxygen).
In some cases (such as water sanitization),ozone production is precisely the point. This requires specialized lamps which do not have the surface treatment.
Short-wave UV light is harmful to humans. In addition to causingsunburn and (over time)skin cancer, this light can produce extremely painful inflammation of thecornea of the eye, which may lead to temporary or permanentvision impairment. For this reason, the light produced by a germicidal lamp must be carefully shielded against direct viewing, with consideration of reflections and dispersed light. A February 2017 risk analysis of UVC lights concluded that ultraviolet light from these lamps can cause skin and eye problems.[5]
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