What is UVC?
UVC is the ultraviolet light with wavelengths between 200 – 280 nanometers (nm)
UVC radiation from the sun does not reach the earth’s surface because it is blocked by the ozone layer in the atmosphere. Thus, the only way that humans can be exposed to UVC radiation is from an artificial source like a lamp or laser
UVC is an irradiation source and require due precautions to ensure safe usage.
The UV range of the electromagnetic radiation spectrum extends from 10 nm to 400 nm. Depending on the wavelength and time of exposure, UV radiation may cause harm to the eyes and skin.
Is UVC safe?
The high energy from UVC is absorbed in the cellular RNA and DNA, damaging nucleic acids and preventing microorganisms from infecting and reproducing.
This absorption of UVC energy forms new bonds between nucleotides, creating double bonds or “dimers.” Dimerization of molecules, particularly thymine, is the most common type of damage incurred by UVC light in microorganisms.
Formation of thymine dimers in the DNA of bacteria and viruses prevents replication and ability to infect.
How does UVC work?
Source: American Journal of Infecious Control
If you notice that there are still bacteria and viruses after UVC exposure, it is because UVC does not "kill" bacteria and viruses, but it destroys, changes their RNA and DNA and prevents it to multiply themselves. They will be still alive for sometime.