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Comment by lvs | Hacker News Reader

> Far UVC lights (200 to ~222nm)

OK, these are not safe wavelengths, and whatever you're reading is not right. This is absolutely ionizing radiation. The rate of formation of thymine dimers in this regime is similar to that around 260 nm. That is, it causes DNA damage. Please see Figure 8 below:

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1751-1097....

The logic of the claim that you can destroy a pathogen with UV but not cause damage to human tissues is incongruous. If it kills the pathogen, it also causes radiation damage to human tissues as well. One cannot dissociate these because they are caused by the same photoionization mechanism.

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552051/

> We have previously shown that 207-nm ultraviolet (UV) light has similar antimicrobial properties as typical germicidal UV light (254 nm), but without inducing mammalian skin damage. The biophysical rationale is based on the limited penetration distance of 207-nm light in biological samples (e.g. stratum corneum) compared with that of 254-nm light. Here we extended our previous studies to 222-nm light and tested the hypothesis that there exists a narrow wavelength window in the far-UVC region, from around 200–222 nm, which is significantly harmful to bacteria, but without damaging cells in tissues.

> As predicted by biophysical considerations and in agreement with our previous findings, far-UVC light in the range of 200–222 nm kills bacteria efficiently regardless of their drug-resistant proficiency, but without the skin damaging effects associated with conventional germicidal UV exposure.

So if I'm reading correctly, the 207-nm ultraviolet light simply doesn't make it past the outer (dead) layer of skin.

That's not relevant, and the paper itself doesn't really measure anything pertinent either. Ionizing radiation does not cause molecular ionization that stays in one place. It generates free radicals that propagate in reaction chains. Reducing the penetration depth only increases the volumetric dose.

Correct, but I’d still like to see their data as to what the impact is to eye tissue.

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