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Comment by elil17 | Hacker News Reader

Far UVC is not carcinogenic (most UV is, this is just a specific wavelength that isn't).

Ideally you'd want to use these lamps in environments that our immune systems didn't evolve for, like crowded conference rooms and school classrooms.

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Far UVC is carcinogenic when it reaches living tissue. However, it has a very short mean free path so it doesn't, generally, reach the growing layer of skin. It's less obvious whether exposed mucus membranes (lips, nose, tongue) or the eyes are affected. It probably doesn't reach the lens of the eye, which is good.

I think that is the same thing as saying that Far UVC is non-carcinogenic.

I actually read it as saying far UVC is probably carcinogenic for specific areas of your body (lips, maybe eyes).

I don't know if that's true, but it's what GP suggests to me.

Ok… but hear me out…

Hey guys, look you can treat everyone at Thanksgiving with one for $500, and bonus might not be carcinogenic if it is made correctly!

That is not true. It can cause possibly eye irritation but animal trials have shown that it is not carcinogenic even to mucus membranes, eyes, and thin-skinned areas.

There is a small watery layer covering your cornea, this is enough to impede far UV-C (~222nm is safe, 254nm regular UV-C is dangerous to your eye!)

The tear layer only contributes a little bit--far-UV eye safety is mostly down to the fact that the 222nm only penetrates to outer epithelium (so cells that will be dead in a few days anyway), and the fact that your eyes get very little effective dose if you aren't staring directly into the lamp. You've got eyelids, eyelashes, eyebrows, hair, etc, so the effective dose to your eyes is actually much lower than the dose assumed by most safety standards (ANSI/IES 27.1-22, UL8802), which are fairly conservative. Check out this paper http://onlinelibrary.wiley.com/doi/abs/10.1111/php.13671

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