It is critically important to be aware of what type of UV is being considered for germicidal purposes. The part of the electromagnetic spectrum involved consists of three UV regions:
- UV-A – traditional blacklight used in insect traps and theatrical settings, abundant in natural sunlight and daylight
- UV-B – also present in sunlight, excessive exposure causes sunburn and repeated exposures over time can result in skin cancer; so-called tanning lamps emit UV-B
- UV-C – germicidal lighting, requires strict precautions, damaging to eyes and skin, not present in sunlight
UV-A and UV-B are not virus killers. It is only the UV-C part of the spectrum that can decimate viruses, including COVID-19, when used appropriately. When considering using UV for germicidal purposes, it is important to carefully read all application, safety and caution notices, and make sure the product is emitting UV-C. The information should include exposure requirements, such as the maximum distance between the source and the objects and materials to be exposed, plus the exposure time required for disinfection. If specific information is not available, ask the manufacturer for clarification. If there is insufficient information or it is difficult to understand, do not use the product. Do not expose eyes or skin to UV-C.
There are safety concerns with UV lighting products, particularly those emitting UV-C, which can cause eye and skin damage to both humans and pets. Home furnishings, including wood, plastics and fabrics, can be damaged as well. UV-C must be used carefully, and to complicate matters, there are many unsafe products on the market touting unrealistic claims without listing the dangers that they pose.
With careful precautions and proper knowledge, it is possible to use UV-C products safely, but in order to be effective, exposure time and distance must be correct. Like sunburn, damage to skin and eyes results from being exposed for too long to the light source.
In the home, a good example of UV-C use is the disinfection of air circulating through HVAC systems.
The UV-C sources are usually placed in the return air duct near the heating/cooling coils where they can remove germs from the air as well as kill mold and bacteria that collect on the coils, especially in humid weather. Portable heating, cooling and humidifying equipment may also include a UV-C source to keep both the device and the circulating air germ free.
In addition to requiring a proper dose of UV-C to be effective, germicidal lighting only works via line-of-sight. Reflected light does not kill germs because most reflecting surfaces in homes absorb the critical UV wavelengths. For example, any clothing or masks with folds or wrinkles will not be disinfected in those hidden areas not directly exposed to the light. Viruses hide in the shadows of nooks and crannies.
The bottom line is that use of UV for disinfection is only thoroughly effective when using the UV-C part of the spectrum, and must be carefully done in strictly regulated environments where people are not present, such as healthcare settings, in order to avoid causing more harm than good. Find more information on the ALA website at ALALighting.com/Home/Germicidal-Ultraviolet-Light.