5 ms·

This is really cool! At the start of the pandemic, I researched UVC light as a mechanism to kill the virus. I do want to point out a minor point: >However, the

This is really cool! At the start of the pandemic, I researched UVC light as a mechanism to kill the virus. I do want to point out a minor point: >However, the widespread use of germicidal ultraviolet light in public settings has been very limited because conventional UVC light sources are a human health hazard, being both carcinogenic and cataractogenic conventional UVC is generated by mercury light bulbs and are carcinogenic and cataractogenic BUT about 10 years ago, it became practical to use frequency doubling in LEDs to generate light really close to the mercury light - the LEDs are not carcinogenic and cataractogenic. When you read about UVC effects, you should check what type of light source they are using (mercury vs LED) Also, it is the advancements in silicon manufacturing that has made it cheaper to make new and different LEDs - such as these "far-UVCs". It is pretty legit! There is "a lot" of research demonstrating effectiveness of "conventional UVC", but not a lot on "far-UVC". One of the limitations on both is the shadow effect... got to go. I'll elaborate if there is interest

detaro 5y ago
> BUT about 10 years ago, it became practical to use frequency doubling in LEDs to generate light really close to the mercury light - the LEDs are not carcinogenic and cataractogenic. What makes the LED light not dangerous that way? As far as I understand, what makes UVC effective is also what makes it dangerous.
- Gibbon1 5y ago
  I did the same as the parent. The answer is that mercury based UV lamps produce a spiky broad spectrum including emission lines really where you don't want them. And not very much at the frequency that is most effective at destroying RNA/DNA. 220nm is important because it's very effective at cross linking thymine. UV LEDs can be manufactured to produce a very narrow spectrum centered on 220nm. So with an LED the total amount of UV produced is much less and doesn't include problematic frequencies that cause eye and tissue damage. Supposedly, I don't work in this space. Note most UV LED's aren't suitable for sterilization. If it comes in a plastic case and costs 30 cents, it's certainly not.
  - ecesena 5y ago
    > UV LEDs can be manufactured to produce a very narrow spectrum centered on 220nm Does anyone know of any manufacturer? I don't think they exist yet?
    - mrsulaj 5y ago
      Full disclosure: I'm the founder of UVX Inc., a University of British Columbia company integrating Far-UVC technology into smart devices. Unfortunately, current state-of-the-art UV LEDs do not produce enough power at the 220nm wavelength to be commercially viable. The current state-of-the-art uses KrCl excimer lamps to generate this light, with optical filters to eliminate spillage in the undesired frequencies (> 230nm).
      - Gibbon1 5y ago
        Thanks for the reply. > KrCl excimer lamps https://en.wikipedia.org/wiki/Excimer_lamp https://en.wikipedia.org/wiki/Excimer_lamp
CryptoPunk 5y ago
>>of the limitations on both is the shadow effect... got to go. I'll elaborate if there is interest Yes please
- rapjr9 5y ago
  Not the OP but the shadow effect is that the light can only kill viruses if it reaches them directly. So if the virus is on your skin under your clothes or in your nose or behind a sofa, the light can't reach it. If the virus is embedded in dirt or opaque oils the light can't reach it. If you're in a crowded room and there is a temporary display that was put up everyone in the shadow of it is not protected as much. Every shadow is a place the virus can lurk, on a surface or in the air. Putting far UVC LED's in places like air conditioners and HVAC systems may make some sense. Putting them in rooms may not, although they would reduce risk to some extent, even though they won't have full coverage. The safety of far-UVC has not been extensively tested, yet it is already being deployed: https://theblindhorse.com/the-blind-horse-becomes-first-restaurant-in-the-united-states-to-install-far-uvc-light-technology-for-real-time-virus-mitigation-and-indoor-sanitization/ https://theblindhorse.com/the-blind-horse-becomes-first-rest...
  - 323 5y ago
    An amount of light will be reflected by the walls. So it will get to most shadowed places too. Of course, a much larger exposure time will be needed to be effective there. You can easily check that there is no true pitch black shadow open place in a room, this is the whole idea behind "global illumination rendering".
    - bratwurst3000 5y ago
      If it reflects at the walls it looses energy and isnt UVC anymore …maybe uvb …. Thats the reason we can see uv floruelenc … 300nm( UVA) radiation that gets reduced to something like 350nm(blue light)
      - 323 5y ago
fsh 5y ago
If the light emitted by the LEDs is "really close" to the mercury light, it should be just as carcinogenic. I also seriously doubt that the LEDs are based on silicon since indirect bandgap semiconductors make horribly inefficient light sources. Also the bandgap of silicon is somewhere in the near infrared. Frequency doubling requires exteremely high intensites that are usually only reached by focussed laser beams. I don't see how one could use it in a LED.
bratwurst3000 5y ago
Hmmm sorry that doesnt seem right. If it is the same wavelength it should have the same properties. You can add waves so that they add up to a new wave. But it is still a uv wave. Maybe the intensity is less…. :). Or the range of uv is more specific.
aaaaaaaaaaab 5y ago
>the LEDs are not carcinogenic and cataractogenic Lol! Yeah, UV light from mercury gives you cancer, but the same electromagnetic radiation from LEDs is totally harmless! LEDs are green, haven’t you heard?
- kadoban 5y ago
  You can say the same thing without being mean.
- mensetmanusman 5y ago
  Mercury excitation produces many more wavelengths of emission that are harmful: http://zeiss-campus.magnet.fsu.edu/articles/lightsources/mercuryarc.html http://zeiss-campus.magnet.fsu.edu/articles/lightsources/mer... A single wavelength emission from a far-UVC led source is therefore safer.
baskethead 5y ago
Far-UVC is UVC light that still kills viruses and bacteria but get absorbed by the top layer of skin and cause no issues. It’s safe for eyes and skin. I don’t know why it hasn’t been productive since the start of the pandemic.

detaro 5y ago

> BUT about 10 years ago, it became practical to use frequency doubling in LEDs to generate light really close to the mercury light - the LEDs are not carcinogenic and cataractogenic. What makes the LED light not dangerous that way? As far as I understand, what makes UVC effective is also what makes it dangerous.

Gibbon1 5y ago
I did the same as the parent. The answer is that mercury based UV lamps produce a spiky broad spectrum including emission lines really where you don't want them. And not very much at the frequency that is most effective at destroying RNA/DNA. 220nm is important because it's very effective at cross linking thymine. UV LEDs can be manufactured to produce a very narrow spectrum centered on 220nm. So with an LED the total amount of UV produced is much less and doesn't include problematic frequencies that cause eye and tissue damage. Supposedly, I don't work in this space. Note most UV LED's aren't suitable for sterilization. If it comes in a plastic case and costs 30 cents, it's certainly not.
- ecesena 5y ago
  > UV LEDs can be manufactured to produce a very narrow spectrum centered on 220nm Does anyone know of any manufacturer? I don't think they exist yet?
  - mrsulaj 5y ago
    Full disclosure: I'm the founder of UVX Inc., a University of British Columbia company integrating Far-UVC technology into smart devices. Unfortunately, current state-of-the-art UV LEDs do not produce enough power at the 220nm wavelength to be commercially viable. The current state-of-the-art uses KrCl excimer lamps to generate this light, with optical filters to eliminate spillage in the undesired frequencies (> 230nm).
    - Gibbon1 5y ago
      Thanks for the reply. > KrCl excimer lamps https://en.wikipedia.org/wiki/Excimer_lamp https://en.wikipedia.org/wiki/Excimer_lamp

CryptoPunk 5y ago

>>of the limitations on both is the shadow effect... got to go. I'll elaborate if there is interest Yes please

rapjr9 5y ago
Not the OP but the shadow effect is that the light can only kill viruses if it reaches them directly. So if the virus is on your skin under your clothes or in your nose or behind a sofa, the light can't reach it. If the virus is embedded in dirt or opaque oils the light can't reach it. If you're in a crowded room and there is a temporary display that was put up everyone in the shadow of it is not protected as much. Every shadow is a place the virus can lurk, on a surface or in the air. Putting far UVC LED's in places like air conditioners and HVAC systems may make some sense. Putting them in rooms may not, although they would reduce risk to some extent, even though they won't have full coverage. The safety of far-UVC has not been extensively tested, yet it is already being deployed: https://theblindhorse.com/the-blind-horse-becomes-first-restaurant-in-the-united-states-to-install-far-uvc-light-technology-for-real-time-virus-mitigation-and-indoor-sanitization/ https://theblindhorse.com/the-blind-horse-becomes-first-rest...
- 323 5y ago
  An amount of light will be reflected by the walls. So it will get to most shadowed places too. Of course, a much larger exposure time will be needed to be effective there. You can easily check that there is no true pitch black shadow open place in a room, this is the whole idea behind "global illumination rendering".
  - bratwurst3000 5y ago
    If it reflects at the walls it looses energy and isnt UVC anymore …maybe uvb …. Thats the reason we can see uv floruelenc … 300nm( UVA) radiation that gets reduced to something like 350nm(blue light)
    - 323 5y ago

fsh 5y ago

If the light emitted by the LEDs is "really close" to the mercury light, it should be just as carcinogenic. I also seriously doubt that the LEDs are based on silicon since indirect bandgap semiconductors make horribly inefficient light sources. Also the bandgap of silicon is somewhere in the near infrared. Frequency doubling requires exteremely high intensites that are usually only reached by focussed laser beams. I don't see how one could use it in a LED.

bratwurst3000 5y ago

Hmmm sorry that doesnt seem right. If it is the same wavelength it should have the same properties. You can add waves so that they add up to a new wave. But it is still a uv wave. Maybe the intensity is less…. :). Or the range of uv is more specific.

aaaaaaaaaaab 5y ago

>the LEDs are not carcinogenic and cataractogenic Lol! Yeah, UV light from mercury gives you cancer, but the same electromagnetic radiation from LEDs is totally harmless! LEDs are green, haven’t you heard?

kadoban 5y ago
You can say the same thing without being mean.
mensetmanusman 5y ago
Mercury excitation produces many more wavelengths of emission that are harmful: http://zeiss-campus.magnet.fsu.edu/articles/lightsources/mercuryarc.html http://zeiss-campus.magnet.fsu.edu/articles/lightsources/mer... A single wavelength emission from a far-UVC led source is therefore safer.

baskethead 5y ago

Far-UVC is UVC light that still kills viruses and bacteria but get absorbed by the top layer of skin and cause no issues. It’s safe for eyes and skin. I don’t know why it hasn’t been productive since the start of the pandemic.