[toomuchtodo]

I'm curious if plastics embrittlement is a problem with Far-UVC. I recently was putting a large evaporative humidifier [1] through its paces for someone to get my opinion, and a challenge was that you had to clean the water tank that was the foundation of the unit fairly frequently (every few days). I provided feedback to the manufacturer that a far UVC bulb in the tank might be useful for reducing cleaning intervals.

For use cases where the emissions are contained (HVAC, water tanks, etc), I think it's a slam dunk from an electronic antiseptic perspective. UV is somewhat common in water filtration today, but perhaps an improvement is possible if these bulbs last longer than existing UV solutions.

[1] https://levoit.com/collections/humidifiers-diffusers/product...

(I do not recommend the humidifier by the way, simply too much work to keep the water tank and the evaporation panels clean, I recommend an ultrasonic version instead)

[elil17]

I do not believe that there is a good understanding of the impact of far-uvc on plastic embrittlement.

[vbelenky]

Two studies that I'm aware of, but yeah, data is thin on the ground:

https://www.mdpi.com/2076-3417/13/7/4141 https://www.boeing.cn/cti/downloads/Boeing-Compatibility-of-...

Summarized here, along with other materials considerations: https://blueprintbiosecurity.org/u/2025/06/Blueprint-for-Far...

[toomuchtodo]

Delightful, an experiment to be run!

[TeMPOraL]

There's research to be done

On the people who are

Still alive.

♫♪

[SV_BubbleTime]

Along the same lines… where is the proof that as the unit ages it doesn’t leave the magic 220nm range?

It is complete nonsense to point this at people.

[vbelenky]

Here's a paper: https://www.jstage.jst.go.jp/article/lsj/50/7/50_394/_pdf

This is a study of the Ushio Care222 unit, but its underlying physics is the same as any other KrCl excimer lamp, so its pretty implausible for other KrCl lamps to exhibit spectral drift when this one doesn't.

The spectrum does change a bit over time--it actually gets less dangerous. But it's a very slight difference.

[SV_BubbleTime]

So different hardware, a clinical unit designed for thousands of hours.

Vs a very likely Shenzen unit that a teeny tiny group is selling on a basic website. And, you can make zero claims on whether a light spectrum of a led will go up or down over time despite one example. Amplifiers/voltages, coatings wearing down, oxide layers in diodes breaking down, etc.

[vbelenky]

I'm not sure what you mean by clinical unit--the ushio care222 is the longest lasting KrCl emitter I'm aware of, but as all bulbs age, they tend to degrade just by losing output, not by spectral shifting.

Basically everyone in far-UVC is a teeny tiny group selling lamps on basic websites, even those who source care222 emitters from USHIO. It's not a big industry!

We don't source our KrCl bulbs from Shenzen, but not for this reason. Yes, that's true about LEDs, but the physics of LEDs and excimer bulbs are different. Excimer spectra don't smoothly shift the way LED spectra do. Excimer spectra have characteristic peaks based on the energy levels of the possible gas molecule species present in the filler gas. The main change over time is the gradual reduction of the 259nm Cl2* peak, which is the main peak of concern--so it fails gracefully. Another possibility is the degradation of the dichroic filter coating under thermal stress--but I've only ever observed this in diffused units, none where the filtered glass is open to the air, and that will happen even on an Ushio bulb.

Nukit is our competitor but I doubt very much that any concerning spectral shift will take place over the course of the lifetime of their lamp.

[SV_BubbleTime]

So… you can’t prove that the unit will not shift wavelength into a harmful range. However, I can prove that by not subjecting myself any others to claimed-harmless light that I can prove it will not become be realized to be harmful.

Cool! You missed peak covid hysteria. But, there are people that will never recover/realize. Like the type of lunatic that would subject everyone to one of these for a thanksgiving dinner in 2025.

[elil17]

You also can't prove that your normal lightbulbs won't magically start outputting harmful wavelengths. Best to live in the dark I suppose.

[vbelenky]

Shrug. Nothing is 'harmless', including far-uv. Going outside in the sunshine isn't harmless. The stove in your kitchen isn't harmless. Can you prove your stove isn't going to explode some day and kill you? No, but you don't expect it to, in part because it complies with consensus product safety standards--germicidal UV products have their own standard, UL8802.

Far-uv is relatively new tech so it's reasonable to be wary, but I'm persuaded on the merits of evidence. Viruses definitely aren't harmless, and I'd rather not be catching random bugs on the regular if I can avoid it, or worry about my grandma catching flu in the hospital. Everyone has to make reasonable tradeoffs about risks and benefits.