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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

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/products/superior-6000s-smart-evaporative-humidifier-2026 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 10mo ago
I do not believe that there is a good understanding of the impact of far-uvc on plastic embrittlement.
- toomuchtodo 10mo ago
  Delightful, an experiment to be run!
  - TeMPOraL 10mo ago
    There's research to be done On the people who are Still alive. ♫♪
- vbelenky 10mo ago
  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.mdpi.com/2076-3417/13/7/4141 https://www.boeing.cn/cti/downloads/Boeing-Compatibility-of-Aircraft-Interior-Surfaces-with-222-nm-Far-UV-Light-Exposure.pdf 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-UVC-V1.0-9.22.25.pdf#page=134 https://blueprintbiosecurity.org/u/2025/06/Blueprint-for-Far...
SV_BubbleTime 10mo ago
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 10mo ago
  Here's a paper: https://www.jstage.jst.go.jp/article/lsj/50/7/50_394/_pdf 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 10mo ago
    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 10mo ago
      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.

elil17 10mo ago

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

toomuchtodo 10mo ago
Delightful, an experiment to be run!
- TeMPOraL 10mo ago
  There's research to be done On the people who are Still alive. ♫♪
vbelenky 10mo ago
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.mdpi.com/2076-3417/13/7/4141 https://www.boeing.cn/cti/downloads/Boeing-Compatibility-of-Aircraft-Interior-Surfaces-with-222-nm-Far-UV-Light-Exposure.pdf 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-UVC-V1.0-9.22.25.pdf#page=134 https://blueprintbiosecurity.org/u/2025/06/Blueprint-for-Far...

SV_BubbleTime 10mo ago

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 10mo ago
Here's a paper: https://www.jstage.jst.go.jp/article/lsj/50/7/50_394/_pdf 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 10mo ago
  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 10mo ago
    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.