[bsder]

> 222nm is not safe to shine on anyone! It will definitely cause skin cancer.

The whole point of using 222nm is that it doesn't cause effects on either the eyes or the skin. Consequently, you can use it at higher concentrations without worrying about the leakage.

The issue, as I understand it, is simply that we don't have a decent LED monochomatic source. All of the currently available sources have broad spectrums that have to be filtered out.

[hedora]

The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

On top of that, reasonable disinfectant timeframes are a few minutes to a few hours, tops. Safety timeframes for human exposures need to be measured in decades if this technology catches on. Claims that lethal dosages of 222nm will penetrate typical glops of pathogens in the environment in seconds, but that cancer causing dosages will not penetrate human skin over years are extraordinary.

Extraordinary claims require extraordinary evidence. Are there long term safety trials for this technology? The article claims “reduced damage” in the abstract, implying routine 222 nm exposure is unsafe.

[bsder]

> The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

It penetrates single cell walls but nothing deeper.

People are mostly interested in 222nm for doing things like sterilizing air circulation and handheld wands. You can put a very high flux without worrying about accidentally exposing someone to a hazardous level of UV light.

People aren't trying to sterilize skin directly (as far as I know), but, even there, it might help healthcare workers. Washing your hands or coating it with alcohol is nasty over time. Being able to hold your hands in a device for 15 seconds and sterilize it rather than having to dump alcohol on them could be an improvement.

[hedora]

"Airborne" viruses are almost always traveling in protective droplets of fluids, sloughed cells, etc, etc. Direct contact with air kills them. So, how does the UV get inside the droplet so that it can reach the pathogen?

[iggldiggl]

Apart from the human safety factor, I'm also curious what it does to other stuff typically found in houses? Even if you were to run the disinfection cycle only while the room is unoccupied, it still affects everything else in the room.

So is the combination of 222 nm + exposure times required for disinfection still enough to cause noticeable bleaching of paints, aging of plastics, etc. etc. over time?

[scotty79]

It's basically because viruses and harmful bacteria are smaller than our dead skin layer. So the light gets into them and destroys their DNA/RNA.

[harvie]

but viruses and bacteria are probably never traveling alone. imagine someone sneezing on table. they will be embeded in pieces of dead skin or tiny droplets of phlegm, saliva, etc... in the linked article they are using it to disinfect surfaces in passenger aircraft. unless it can penetrate a bit, i don't see how it can be effective.

also viruses (eg. HIV, Coronavirii,...) are often killed by oxygen in air, dry out or die in other ways when not floating in bodily fluids.

[jefftk]

The light doesn't need to kill 100% of pathogens to be effective at decreasing risk. I agree that if the pathogen is on a table but under a protective layer the levels of UVC we're talking about aren't going to do anything to it. But the main concern is with airborne viruses which mostly aren't very protected.

[lightedman]

Sadly, not even LEDs are truly monochromatic and typically have a ~20nm spread on either side of the peak. They also exhibit drift in wavelength peak. This is seen at my job, where I run the UV testing and production.

[scotty79]

I don't think it needs to be monochromatic. If the longest wavelength is 222nm, other penetrate skin even less.

[jefftk]

The longest wavelength isn't 222, that's the peak wavelength.

KrCl excimer lamps produce a relatively narrow spectrum as is: https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041

If it turns out we need it to be even narrower, we could put filters on them.