The key here is the 'far' range of UV (220–400). Like regular UVC (100-400), it kills viruses and bacteria. There have been UV light sterilizers in biology labs since at least the 60s (first time I ever saw one) but those were enclosed, baffled fans pulled air in, moved it past the lamp(s), let it flow back out.

UVC is dangerous; it will give you skin and corneal burns in fairly short order. We earth-dwelling creatures are not evolved for it as it does not make its way through the atmosphere to the ground.

The shorter the wavelength, the less a light (or anything waveform) can penetrate (one of the reasons old-style portable phones had better range than modern ones is that they used a longer wavelength and so had better penetration through walls, etc.)

Far UVC is short enough that it cannot make its way through the top layer of dead cells than makes up our skin - or through the layer of tears over our corneas. That's the reason people are getting excited about it. There are fluorescent far-UVC lamps now. LEDs are hopefully coming. Anything you buy on eBay as 'far UVC' is probably not. You might find one listed by nm. I've bought a couple that are supposedly 220nm, but I don't have access to a spectrometer that works in that range, so I can't verify them. I have had snow blindness (cornea sunburn) in the past. It's quite unpleasant. I’d rather not test on my corneas.

I suspect the reason far-UVC LED development stalled is that we thought covid was transmitted in droplets (hence the 6ft separation) and by touch. It wasn't clear far-UVC could penetrate droplets. We were late in determining that transmission was primarily by aerosol (like measles).

Could I trouble you to change the "UVC doesn't effect our skin" caption? BTW, it's 'affect' - and it really does have an effect (process / result - pedant hat off)

Also, apologies for coming on so strong, but this is something I've been tracking for a couple of years now...