Thread by @fergal_whatever

Intro to far-UVC air-cleaning from a non-expert.
Ultraviolet light has been used to sterilise objects for decades and has been used to clean air in rooms since the 1940s, with TB being a big driver of that.
It's called UR-UVGI - upper-room UV germicidal irradiation.

That kind of UV light is harmful to humans, causing "sunburn", skin cancer and cataracts. That's why it's "upper room", you shine it away from the humans. Of course that means you have to wait for the bugs to float up there to kill them. Warm air rises, so they do get up there.

Recently we have far-UVC light which is a higher frequency (222nm). It's just as effective at killing bugs but "harmless" to humans.
"Harmless" here is still kinda new, so don't go staring at these lights for hours on end.
nature.com/articles/s4159…

There are recommended exposure limits. Depending on power and distance, the limit is hours or even days. So we can kill corona, flu, TB etc in public spaces from the moment it's exhaled,. No waiting for it to float to the right place.
Lots of info here.

The lamps are still pretty expensive but production is ramping up, so prices will come down. That said, demand may also ramp up, so it could be a few years before prices really drop.

I've been looking at various manufacturers recently, particular in China.
First UVC's news page says they were visited by the head of China's corona task force.
That's more evidence that China is betting big on this for their end game.
firstuvc.com/article/32.html

Also I think their lamps were used by the Chinese Olympic team in Japan.
(Thanks for the Chinese propaganda warning Twitter!)

https://twitter.com/fergal_whatever/status/1542670438005821440

They make a range of lamps, including a personal USB/battery powered lamp!
It costs $260USD.
I don't know enough about the details on this to tell whether a 5W lamp like this is gimmick or could actually keep you safe in a restaurant.
firstuvc.com/product/9.html

Most of their room-fixture lamps are $1000USD-$3000USD.
Other companies like Care 222 (Ushio in Japan) are a bit more expensive, however I would probably trust them for safety a bit more.

care222.com

Gimmicks aside, this seems like the future. Clean air just like clean water, although when going on holidays "don't breathe the air" is going to be a bit more of a challenge than "don't drink the water"!

Addendum:

Here's a paper where they found that far-UVC was doing the equivalent of 184 ACH. I.e. It reduced the viral load like a ventilation system that replaces or filters the air in the room 184 times per hour. That'd be a wind-tunnel!
nature.com/articles/s4159…

They did this with 5 lamps installed in the ceiling, in a room 4.26m x 3.35m x 2.26m. It doesn't what wattage the lamps were but being in the room for 8 hours would still leave you below the recommended daily exposure limit.

So the headline is 36 ACH (184/5=36). That's probably about $3000 of lamp to get 36 ACH equivalent in a 14sqm room. Kinda pricey but doing that with HEPA or ventilation would be completely impractical and maybe even more costly.