The sun emits optical radiation in form of visible and invisible light. We humans define light as what we can see from the visible spectrum of light, that is, the wavelength between violet (400nm) and dark red (800nm). For the use of light against viruses and germs, the focus is on the range below 400 nanometers, the so-called UV radiation. UV light is divided intro three ranges: UV-A, UV-B and UV-C. The wavelength decreases progressively from 400 to 100 nanometers.
Category A ultraviolet sunlight reaches the earth almost unfiltered. UV-A radiation penetrates deep into our skin and causes it to age. UV-B light reaches our upper skin layers and is responsible for sunburn. The short-wave, particularly high-energy UV-C radiation from the sun, on the other hand, is completely absorbed by or ozone layer. There is therefore no natural UV-C radiation on earth. Life on earth has thus developed without being exposed to UV-C radiation. In other words: There was simply no need to develop natural defense mechanisms against UV-C light. This opens special possibilities for science, medicine and technology.
UV-C photons with a wavelength of 200 to 280 nanometers have sufficient energy to alter microbial DNA meaning the exposure to the electromagnetic radiation modifies the genetic material of microorganisms and disrupts their ability to reproduce. As UV-C radiation attacks the helix structure of DNA and RNA it is also effective to inactivate multi-resistant pathogens.
For the use of light to inactivate pathogens, the focus is on invisible light below 400 nanometers, the so-called UV radiation, in particular the Category C ultraviolet light. Although both UV-B and UV-C can harm cells and hence have the capability for sanitization, the extent of the molecular rearrangement of the DNA / RNA by these two radiations is very dissimilar. The shorter the wavelength as more effectively light can penetrate the cells of Microorganisms, therefore UV-C is more suitable to neutralize pathogens. UV-C radiation triggers a photochemical reaction. Depending on the doses of the absorbed UV-C light it modifies the DNA / RNA helix strands by thymine dimer formation, disrupting the pathogen’s capability to replicate and render it harmless.