Comment by gpm
25 days ago
I'm confused by the handwaving away of the ozone production. It's well established that ozone is toxic. If these are producing it - and it seems to be agreed upon that they are - that's an obvious issue. The suggestion that "you can just filter it with mechanical air filters (activated carbon)" seems strange because you can just filter viruses with mechanical air filters in that case...
I'm a big fan on the idea of improving air quality/reducing viral load in air to improve health. But I'd really prefer to see more of a push towards the "effective quiet (currently DIY) mechanical air filtration systems" the article links to then a technology with obvious and poorly quantified health risks.
From Aerolamps website:
>Does Aerolamp produce ozone? >Yes - but only a very small amount
>Typical indoor ozone levels are 4-6 parts per billions (ppb), while average levels of outdoor ozone are 20-30 ppb - almost all indoor ozone comes from outdoors. Most likely, you will raise your indoor ozone levels much more by opening a window than by operating a far-UVC lamp.
>It's true that in a sealed chamber in a lab, typical far-UVC installations might produce significant (10s of ppb) ozone. However, our indoor spaces aren't sealed chambers. Both theoretical predictions and experimental evidence suggest that Aerolamp will raise indoor ozone levels by no more than 1-2 ppb. Expected ozone increase can also be simulated with Illuminate.
>However, we recognize that ozone is a pollutant, and recommend that Aerolamp should be used with portable air cleaners which include an activated carbon filter. Studies suggest that a single activated carbon filter is more than sufficient to mitigate any far-UVC derived ozone.
I agree that the filter thing doesn't make sense, but it does not seem like this product would meaningfully increase your ozone exposure.
You can filter viruses with mechanical air filters, but based on the available data, far-UVC can do this much faster than even a high-CADR air filter. The best filter I'm aware of can deliver 200 CFM of clean air quietly or 400 CFM loudly, one high-quality far-UV lamp can deliver the equivalent of ~1000 CFM--silently. That seems like the main advantage to me--plus not taking up the floor space that a large, quiet air filter would require. Basically it's the more dakka solution. But it's recommended to use far-UV with at least one source of mechanical air mixing like an air filter anyway just to make sure its maximally effective
Old-school UVC lights do produce ozone, and it needs to be taken care of.
Newer lights (might) use LEDs that do not produce ozone. I only use LED uvc lights. Also, and this is key: DO NOT look at the uvc light. It can damage your eyes. It is safe for your skin, but it is not safe to look at.
This is incorrect, unless by "old school" UVC lights you mean 172nm xenon lamps. Those produce quite a lot of ozone. 254nm UVC lamps (also quite old school) do not produce ozone.
Ozone is produced at wavelengths below 242nm, but at very low levels. Significant ozone production only ramps up at wavelengths below 200nm (note the log scale in the figure https://onlinelibrary.wiley.com/doi/pdf/10.1111/php.13391) Whether or not the light is produced by an LED is immaterial--what matters is the output spectra.
There are no UVC LEDs that I would consider "safe" for either eyes or skin, except insofar as they are safe because they output very little light, or no UVC at all. SilannaUV makes a 235nm LED, but much of its spectrum is outside the relatively safe "far-UV" band.
Krypton-chloride lamps produce near-monochromatic 222nm, and generally are sold filtered to remove even traces of non-far-UV wavelengths. These are relatively safe because at 222nm, protein absorption in the outer layers of human tissues is so high that the photobiological risk is likely low, especially in skin. I still don't recommend staring directly at those lamps for extended periods of time, especially close up, but this is the only kind of lamp that I might consider 'safe'.
Essentially, if it doesn't produce ozone, it is likely a significant photobiological hazard--unless it's just producing very low levels of light, or not producing UVC at all. Many "UVC" lights you can buy online aren't really UVC at all.