We all know about “germs”. Specifically they’re bacteria and viruses that get you sick
You’ve probably seen the visible light spectrum before; on the spectrum, visible light (violet to red) is from 380 nanometers to 780 nm. As a reference, most household lamps are between 500 and 700 nm.You may also be familiar with UVA and UVB (280nm-400nm), related to suntans and sunburns and used in tanning bed applications.
It is generally agreed upon that 254 nanometer UVC is optimal for germ-killing purposes.
At the foundation of a suntan or sunburn is skin cell damage caused by Ultraviolet-A and -B rays given off by the sun. UV rays are harmful. SPF 30, Earth’s atmosphere, and evolution have allowed us and most organisms to develop a tolerance to moderate levels of UVA and UVB. That’s the big difference.
The sun gives off UVC, too, but it’s not strong enough to penetrate Earth’s atmosphere. So, there’s been no chance for infectious bacteria and viruses to develop a similar immunity. Hospitals use UVC to kill germs because its germicidal characteristics can be unequivocally relied upon