Water, air, and foodstuff can be disinfected using ultraviolet light, UV. This radiation destroys bacteria, bacterial spores, molds, mold spores, viruses, and other microorganisms. Radiation at a wavelength of around 254 nm penetrates the cell wall and is absorbed by the cell materials including DNA and RNA stopping cell replication or causing death. The use of UV radiation for disinfection dates back to the 1900s when it was used to a limited extent in disinfecting water supplies.
The low-pressure mercury arc lamp is the principal means of producing ultraviolet light. This is used because about 85% of the light output is monochromatic at a wavelength of 253.7 nm which is within the optimum range for germicidal effect. It should be noted, however, that the optimum range for germicidal effect is also within the UV-B ultraviolet radiation. UV-B is less than or equal to 320 nm and is the dangerous range for causing skin cancer. Thus, it is important that workers be not unduly exposed to this radiation.
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