UV light, or ‘ultraviolet light’, is a form of non-visible electromagnetic light. The main source of UV is the sun. There are three types of UV light: UV-A, UV-B, and UV-C. They’re differentiated by the wavelength of the light, with UV-A light has the largest wavelength, ranging from 315-400nm. UV-C light has the shortest wavelength, from 100-280nm.
How Does UV-C Light Kill Viruses?
As UV-C light has the shortest wavelength, it also has the most energy of the UV light types. That means it’s the most powerful at destroy the genetic material inside viruses and other microbes.
UV-C light at a specific wavelength of 254nm has been found to be most effective in killing coronavirus such as a severe acute respiratory virus (SARS-CoV) and Middle Eastern Respiratory Syndrome (MERS-CoV) as well as other viruses like H1N1 influenza.
More detailed data and knowledge about using UV light kill virus check ‘Common UV Lights Aren’t Great at Killing COVID-19’ and ‘UV Light Disinfects Masks, Harms Filtration Less Than 2%‘
Is UV-C Light Safe?
Most of the UV-C light produced by the sun is absorbed in the atmosphere, so our bodies and skin rarely receive much of it. That’s a good thing since UV-C light is considered harmful to the body.
UV lights used for disinfection generate UV-C with wavelengths in the range of 254-265nm. This wavelength is great at destroying genetic materials inside viruses. However, that also means it’s good at destroying materials inside our bodies.
UV-C light can cause corneal injuries to the eyes, as well as photokeratitis (a feeling of sand in the eyes). Sunburn and more serious skin cancer can also be caused by UV-C light.
The American Conference of Governmental Industrial Hygienists (ACGIH) recommends a limit of 3mJ/cm2 for UV light in the actinic range (200 nm – 315 nm), which covers UV-C light. For a typical 0.7W UV sanitizer lamp, that means the exposure times at varying distances are shown in the table below:
| Distance from UV light | Time |
| 2m | 171s |
| 1m | 43s |
| 50cm | 11s |
| 10cm | 0.4s |
Direct contact with UV-C light should be avoided. If working with it, it should only be dealt with when using protective gear such as protective glasses and clothing.
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