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An ultraviolet (UV) germicidal lamp is a mercury-vapor lamp that emits short range ultraviolet rays with a wavelength of approximately 254 nanometers (0.00001 inches). Short range UV (UVC) breaks molecular bonds in the deoxyribonucleic acid (DNA) of microorganisms, creating mutations that inhibit growth and reproduction. The UV germ light is used to disinfect air and water, purify food, and sterilize items in laboratories and medical settings. A number of factors determine the efficacy of the UV germ light, including the microorganism resistance to UV, the presence of particles that block the UV, power fluctuations that may alter the wavelength, and the duration of exposure. Winning the Nobel Prize for Medicine in 1903 for his innovative method of killing bacteria that cause tuberculosis, Niels Finsen pioneered the use of ultraviolet rays as a germicide, but ultraviolet germicidal light systems became extensively available in the mid-20th century.
Ultra-short ultraviolet light in UVC lights can injure humans, with exposure leading to sunburn and skin cancer. Eye exposure produces painful corneal burns, cataracts, retinal toxicity, and temporary to permanent blindness. UVC generates ozone when it hits oxygen molecules, and while ozone in the stratosphere protects the earth from the sun’s radiation, ozone can be toxic when atmospheric levels exceed .05 parts per million. In most germicidal irradiation systems, the UV germ lamps sit in closed environments, like air circulation systems or water tanks, or have defensive shields that mitigate the risk.
Germicidal irradiation using UV germ lamps can be used in conjunction with filtration systems to sterilize air in forced-air systems, circulating the flow of air in front of a lamp located at the coils or drain pan. Water purification by UV irradiation in waste water treatment facilities has replaced chlorination in many sites, but a potential disadvantage to this method of sterilization is that the water can become contaminated again after the treatment, unlike chlorinated water. The UV germ light has also been used to sterilize fresh juices, like apple cider, and some fruits and vegetables, especially since regulations were passed by the United States Food and Drug Administration in 2001 mandating a reduction in bacteria. Microbiology laboratories commonly sterilize glassware, goggles, instruments, devices and plastics with ultraviolet light. The lights can also control unwanted pathogens in ponds and aquariums.
Multiple passes through a redundant system increase the effectiveness of sterilization using the UV germ light by prolonging exposure to the light. UV bulbs should be replaced each year and cleaned routinely to prevent dust and particulate matter from lowering the UV output. Shielding the lights from direct air flow precludes degradation of the effect by air cooling. Reflection using aluminum also intensifies and strengthens the pathogen-killing effect of the light.