UV-C light damages the DNA molecule of viruses, bacteria, moulds and other microorganisms and with this it kills them or at least prevents its reproduction. There are two different sources of UV-C light, one is similar to fluorescent lamp without the fluorescent medium and the other is LED which emitts light in the UV-C spectrum range. These photons are not visible to the naked human eye, but nevertheless this light is harmful for all living beings, humans, pets and plants. UV-C photons cause demages in skin which results in redness very similar as sunburn so it is necessary to avoid exposure to prevent these effects.
UV-C light with wavelength 254 nm, at which the mercury atoms emit photons is overlapping the absorption peak of DNK (DOI 10.1007/978-3-642-01999-9), which means that this light has germicidal effect on viruses, bacteria and all living organisms, which contain DNA or RNA molecules. UV-C disinfection is especially effective with coronavirus COVID-19.