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Comment by jefftk | Hacker News Reader

None of your links are about 222nm; they're all about longer wavelengths or mixes that include longer wavelengths.

Let's be clear here. Nothing outside of some extremely filtered high end equipment is producing exactly and only 222nm light, and no cancer study is isolating exactly and only 222nm light. Except in extreme cases all light sources have some bandwidth. Most UV generators produce tens to hundreds of nm of bandwidth. A common MIG or TIG welder produces plenty of 222nm light in a broad distribution* of UV. UV lamps for curing applications have used arcs to generate deep UV for ages. Lack of a particular study for a particular 1nm band is not a meaningful signal.

*Source: https://www.ehime-iinet.or.jp/ehime_e/corp/toyo/ronbun/image...

I agree welding is very broad spectrum, including both 222-nm and many other frequencies, and also dangerous. But these KrCl excimer 222-nm products generate light through a completely different mechanism and produce a far narrower spectrum. See https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041 and specifically this chart https://pubs.acs.org/cms/10.1021/acsphotonics.2c00041/asset/...

We do know a lot about how dangerous different frequencies are, and when you combine the "risk to humans" curve with the "emissions by wavelength" curve you get very low risk.

I do still think we should run additional experiments here before rolling this out broadly for hours-a-day usage, but from what we know so far it looks very good.

Perhaps 222nm is absorbed primarily by dead skin cells - but why is skin the only tissue mentioned? It says nothing about damage to corneal and conjunctival tissues. Eye damage is a major hazard for humans with UV light in particular. "Very low risk" simply doesn't track. "Reduced risk" might.

Eyes, like skin, have a layer of dead cells, and sufficiently short wavelengths can't get through. If you shine enough 222-nm into eyes they'll get dry and uncomfortable, but we're talking about much lower levels.

Here's an example of some of the research here, where they shined 222 nm vs 254 nm into rat eyes and looked for corneal damage. While 254 had some harmful effects 222 was fine: https://www.tandfonline.com/doi/abs/10.1080/10715762.2019.16...

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