253nm irradiation (aka UV-C) is considered the most destructive to virus and perhaps even bacterial DNA. Same peak wavelength as the large sterilizations carts used to do hospital rooms. It also happens to be the wavelength of EPROM ERASER lamps. I use my old EPROM eraser to sterilize everything (mostly groceries) that go into my 84 year old moms house. Also intended for the few masks that we have. We use sunglasses that significantly attenuate UV ~95%+. We also have no direct line of sight to the bulb and keep our hands either clear/shaded or gloved to avoid sunburn and messing with the DNA in our skin. A black matt surface is under the light to prevent reflection. The light is quite powerful because you can smell the ozone. Since I am stranded away form home without my light meter and other optiker gear and there is no manual online for this a 30 year old device , I estimated the irradiance from what EPROM’s require and the time we used to put on timer to erase them. Worked out to 7 seconds for viruses. Depending on the unit you have, you may have to remove the tray and possibly even defeat an interlock.
BE ULTRA CAREFUL NOT TO IRRADIATE YOUR SKIN OR GET THE LIGHT IN YOUR EYES. EVEN IF WEARING PROTECTIVE GLASSES, ENSURE YOU ARE PROTECTED FROM OFF AXIS LIGHT AND SPECULAR REFLECTIONS. THE LIGHT WAVELENGTH IS OPTIMAL FOR KILLING VIRUSES, BACTERIA AND IT DOES IT BY MESSING UP THE DNA. IT WILL DO THAT TO YOUR SKIN AS WELL.