The green banana UVC test.
There's three kinds of ultraviolet, A, B and C. For disinfection,
you need the higher frequency UVC. This has more energy per photon, and
that's enough to break up the virus structure, killing it.
If you have a UV light that claims to kill viruses, how can you test it? Have you got a collection of viruses (I do), and even if we do, how can you tell if the light kills them? You do too; there are ten times as many virus and bacteria cells as human cells in your body. But you can't really use them. If it really is UVC, then shining it on your skin will damage your skin.
So you need a fake virus. Oh, this is so similar to a situation I know so well!
Take one unripe banana. Put a stripe of masking tape around it, then put the banana under your UV light. Give it 10 to 15 minutes. When you take it out, peel off the masking tape, and you'll see that the banana has gone brown, except where the masking tape was.
If you do the same test with the fake UV lights (the disco lights that are sold as disinfecting), then the banana doesn't go brown.
It is appalling that so many people are selling fake disinfecting lights. It's like selling fake medicine - except that there's an awful lot of that around too.