UV lamps have been used to inactivate microorganisms for many years. Much of the early work was directed at the control of very infectious microorganisms (particularly Mycobacterium tuberculosis, the causative agent of tuberculosis), often in medical facilities. Wavelengths within the short wave, or C band of UV light (UV-C or UVC), were found to be the most effective germicidal light wavelength. UVC is generated by electrical discharge through low-pressure mercury vapor enclosed in a glass tube that transmits UVC (primary wavelength of 253.7 nm) light. UVC at 253.7 nm is also referred to as UVG to indicate that it is germicidal. UVC has been shown to inactivate viruses, mycoplasma, bacteria, and fungi, whether suspended in air or deposited on surfaces.
Scientists have classified UV radiation into three types – UVA, UVB, and UVC.
The Sun produces UV. The stratospheric ozone layer absorbs some but not all of these types of UV from sunlight:
- UVA Not absorbed by the ozone layer
- UVB Partially absorbed by the ozone layer
- UVC Completely absorbed by the ozone layer
“Ultraviolet (UV) light has long been known to have germicidal properties … UV radiation was one of the earliest recognized methods of disinfection, however its use was discontinued around the the turn of the century because of the advent of chlorination and ozonation. Recently, there has been a renewed interest in UV radiation as an alternative to chemical treatments largely as a result of concern over toxic chemical byproducts.”
– Rensselaer Polytechnic Institute (RPI)