4 ms·

>>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
      If true that would be terrible. Because higher wavelength UV is very dangerous. And are you sure about this? When visible light gets reflected by a wall it doesn't seem to change wavelength significantly (color basically remains the same).
      - bratwurst3000 5y ago
        Okey i wasnt clear. The wall has to interact with the radiation. Thats why you see colours. https://wonderopolis.org/wonder/why-does-a-black-light-make-things-glow https://wonderopolis.org/wonder/why-does-a-black-light-make-...
    - nkmnz 5y ago
      That’s not at all how reflection or fluorescence work. Reflection does not change the wavelength. Fluorescence is a three-step-process of absorption, internal conversion (energy-loss) and re-emittance of light with a higher wavelength. Fluorescence-efficiency is usually very low, and highly specific to the absorbance of a certain wavelength, so unless you have bad luck with the color of your wall, fluorescence should not be of high concern.
      - Tagbert 5y ago
        “re-emittance of light with a higher wavelength” I would say that the re-emitted light has a “longer” wavelength. Fluorescence always produces a longer wavelength. UVC becomes UVB, UVB becomes UVA, UVA becomes blue, etc. Though different materials increase the wavelengths to different degrees. That is why “black lights” can produce different fluorescent colors.
      - bratwurst3000 5y ago
        Hmmm light is a package of photons and when it reflects and the object is blue it looses the blue spectrum(photons) in the package. This package can be disected with furier and should have a different wavelength then befor……. Are you sure thats not how it works?? I would love to be proven wrong. Had not enough physics to fully grasp that concept :) And did you ever use a blacklight in a dark room? Many things are shining. For example teeth. So smilling could get 220nm to a dangerous zone and kill the one that is smiled at? … hehe little joke.
- peterburkimsher 5y ago
  What if the objects to be disinfected could be rotated under the light? I'm imagining a washing machine full of masks (COVID concentrators), beaming UV-C light at them as they spin around. Would that mitigate some of the shadow effect, because they're in motion?
  - Tagbert 5y ago
    Yes as they would likely present different surfaces with each tumble cycle.

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
    If true that would be terrible. Because higher wavelength UV is very dangerous. And are you sure about this? When visible light gets reflected by a wall it doesn't seem to change wavelength significantly (color basically remains the same).
    - bratwurst3000 5y ago
      Okey i wasnt clear. The wall has to interact with the radiation. Thats why you see colours. https://wonderopolis.org/wonder/why-does-a-black-light-make-things-glow https://wonderopolis.org/wonder/why-does-a-black-light-make-...
  - nkmnz 5y ago
    That’s not at all how reflection or fluorescence work. Reflection does not change the wavelength. Fluorescence is a three-step-process of absorption, internal conversion (energy-loss) and re-emittance of light with a higher wavelength. Fluorescence-efficiency is usually very low, and highly specific to the absorbance of a certain wavelength, so unless you have bad luck with the color of your wall, fluorescence should not be of high concern.
    - Tagbert 5y ago
      “re-emittance of light with a higher wavelength” I would say that the re-emitted light has a “longer” wavelength. Fluorescence always produces a longer wavelength. UVC becomes UVB, UVB becomes UVA, UVA becomes blue, etc. Though different materials increase the wavelengths to different degrees. That is why “black lights” can produce different fluorescent colors.
    - bratwurst3000 5y ago
      Hmmm light is a package of photons and when it reflects and the object is blue it looses the blue spectrum(photons) in the package. This package can be disected with furier and should have a different wavelength then befor……. Are you sure thats not how it works?? I would love to be proven wrong. Had not enough physics to fully grasp that concept :) And did you ever use a blacklight in a dark room? Many things are shining. For example teeth. So smilling could get 220nm to a dangerous zone and kill the one that is smiled at? … hehe little joke.
peterburkimsher 5y ago
What if the objects to be disinfected could be rotated under the light? I'm imagining a washing machine full of masks (COVID concentrators), beaming UV-C light at them as they spin around. Would that mitigate some of the shadow effect, because they're in motion?
- Tagbert 5y ago
  Yes as they would likely present different surfaces with each tumble cycle.