Is there any reason why they can't just be installed inside air purifiers/ventilation?

Especially since you could probably get more mileage out of the same amount of light energy by forcing the air through a narrower passage, since only airborne particles are actually going to absorb any energy anyway, and air is mostly just empty air.

Yeah I saw a lamp for this and it had a proximity sensor to prevent overexposure. There's no way I'm buying a lamp that needs that to be safe. Especially if it's expensive and only lasts a year or two.

Every year our HVAC company tries to sell us UV lights for the HVAC system. They claim it's only about $1500 to install. Are these snake oil?

Could accumulate in an isolated room, but following normal building ventilation standards, really shouldn't be an issue as shown by Brenner in 2023: https://pubmed.ncbi.nlm.nih.gov/38037431/

Yes, few people have AC but almost everyone living in a semi recent place has mechanical ventilation in, at the very least, kitchen and bathroom, which thanks to physics renew the air of the entire falt/house.

This is correct and such systems do exist, sometimes combined with sources of ions and HEPA filters. However if you're already drawing air out of the room, it's easier to just filter it with HEPA than dealing with the additional complexity of UV lights (deterioration, energy consumption, replacement).

Still risky, these typical Chinese devices don't come with a filter, so harmful wavelengths will still be present. The filter is actually the expensive part. Also, such a small component would need sufficient cooling as these operate at 4kV. I don't really see this here, so it makes me doubt these devices.

The germicidal effect is a function of the DNA being directly affected by the UV rays and breaking apart. Very few organisms exist that could adapt, this would require external shells, skin etc, not typically found in microorganisms.

There is a giant orb in the sky that emits UV and has for billions of years.

I think the microbes are still trying to figure this one out.

I also wonder about stuff like this. I think some things are just a bridge-too-far for organisms to evolve protections against. For instance, are we worried about using too much bleach? Or stepping on cockroaches?

I doubt it would be a problem for the microbiome [1] but I would worry about the immune system. Would being inside in sterilized air all the time mean you can't go outside or into a forest without getting really sick?

[1] but who am I, it would still be worthwhile to check obviously

I would consider it unlikely that airborne germs form a significant input to our microbiomes.

For example, the gut microbiome is in flux for about the first 3 years of life, and thereafter it's mostly only the relative abundances of different microbes that shift in response to diet, you need something like antibiotics or severe diarrhea to actually induce permanent changes (usually for the worse).

Compared to that, there really aren't many microbes in the air. For children, it could very possibly be bad, but even then I'd expect most of their microbial input to come from their parents, food, and surfaces. Which are already grossly deficient compared to old-school rural settings, but I'm not sure if germicidal UV would make it worse.

Studying a building's microbiome is really a new field. What happens to people if offices become boxes of sterile air and -surfaces? We don't know.

> What about beneficial and neutral but important bacteria and viruses?

Such as what? There are some located in the gut, but pretty much everything else out there is in conflict with our immune system.

too much UV all at once, you mean. melanoma is not common and face and arms - the regions which receive the most sunlight

a moderate amount of UV stimulates vitamin D production, suppresses inflammation, and turns on DNA repair pathways

The article explains this concern in the 3rd and 4th paragraph.

Wong UV wavelength range! 222nm is safe for humans [0]!

[0]: https://www.nature.com/articles/s41598-020-67211-2

Far UVC?