But 405 nm shouldn’t be a significant issue, especially with LEDs. That’s within the visible spectrum, and if visible light was going to kill us we’d have noticed by now. If the flux is alarmingly high, sunblock and sunglasses should do it.
Your link seems to be dead. But I’m not too worried about that; an ordinary person will respond to uncomfortable levels of visible light by squinting, looking away, wearing sunglasses, etc. without expert intervention.
I think I may have been unclear; I wasn’t saying “let’s not use blue light for anything” or anything like that, just giving a bit of context. It shouldn’t be so surprising that blue light can kill some microorganisms, given that it can harm humans too.
The germicidal flux from the paper is 155.8 mW/cm^2, which is much stronger than sunlight which is about 0.1 mW/cm^2/nm at sea level for short wavelength visible light. I don’t know what your threshold for alarming is, but to me that seems high enough that concern is warranted. And I’m not sure that conventional sunscreen would actually help. Based on this overview of sunscreen, it looks like most broad spectrum sunscreens don’t do much above 380 nm or so.
Also, It doesn’t seem clear to me that the fact that blue light is visible implies it’s not harmful. (UV is harmful, and some species of bird and rodent can see ultraviolet light, as can some humans.) What’s your reasoning? It is definitively known that UVA light is carcinogenic by an indirect oxidative stress mechanism, and I can’t find any discussion of at what wavelength exactly this mechanism stops being relevant. Because the mechanism for germicidal action for 405 nm light (described in the linked paper) is also oxidative stress, it seems very likely that 405 nm light is carcinogenic for exactly the same reason as UVA, although possibly less so.
If your flux is 1,558 times that of sunlight, that’s definitely alarming. At that point, the wavelength might not matter very much; you might be dumping enough energy to sterilize surfaces by heating.
The paper indicates that the treatment generally works by stimulating porphyrins in bacteria or fungi of interest. Humans can have light sensitivity due to porphyrins, a condition called porphyria, but it’s fairly rare. Unless the novel coronavirus has porphyrins in its chemistry, I wouldn’t expect to this effect on the virus, as the paper notes. The reported data indicate that the effect is dependent on other elements of the mixture; something else in the solution may break down under the flux and attack the virus.
My reasoning was basically similar to this sentence from the paper: An alternative mechanism of inactivation when FCV is suspended in MM may be associated with the LED emission spectrum extending slightly into the UVA region, meaning the virus is exposed to very low-level UVA photons (~390 nm).
To be clear, those two units are different. 155.8 mW/cm^2, and 0.1 mW/cm^2/nm. So it’s not 1,558 times stronger than sunlight overall. Neglecting atmospheric effects, sunlight across all wavelengths is 135 mW/cm^2, so about the same total flux—it’s like we compressed the broad spectrum of sunlight to all be a single wavelength. My point is that it’s much much more blue-violet light (not much much more light total) than what we usually encounter. Blue-violet from sunlight may be safe for our skin, but that doesn’t necessarily imply that blue-violet light at germicidal intensity is safe.
Unless the novel coronavirus has porphyrins in its chemistry, I wouldn’t expect to this effect on the virus, as the paper notes.
This is an important point. Germicidal blue-violet would likely be ineffective against airborne viruses.
The reported data indicate that the effect is dependent on other elements of the mixture; something else in the solution may break down under the flux and attack the virus.
This is exactly my concern. What’s to say that the reactive chemical species that “attack” the virus won’t also be a problem for human cells? The mixture in which blue-violet light is more effective was made of “artificial saliva, artificial faeces and blood plasma,” so whatever is breaking down could break down exactly the same way in our bodies.
(To be clear, I’m not saying it’s necessarily unsafe for human skin. I’m just saying we shouldn’t assume it is safe.)
DNA has an absorption peak at 254 nm. Light of that wavelength or below causes chemical changes to DNA that are fatal to any organism.
This is also (very nearly) the maximum absorption of the ozone molecule. The formation of the ozone layer seems to have been a prerequisite to non-aquatic life.
But 405 nm shouldn’t be a significant issue, especially with LEDs. That’s within the visible spectrum, and if visible light was going to kill us we’d have noticed by now. If the flux is alarmingly high, sunblock and sunglasses should do it.
It’s not going to kill us. But high-intensity blue light will, in the long term, damage your retinas. See e.g. http://photobiology.info/Rozanowska.html .
[EDITED to fix a typo in the URL; sorry about that]
Your link seems to be dead. But I’m not too worried about that; an ordinary person will respond to uncomfortable levels of visible light by squinting, looking away, wearing sunglasses, etc. without expert intervention.
Oops! The perils of hand-transcribing URLs.
I think I may have been unclear; I wasn’t saying “let’s not use blue light for anything” or anything like that, just giving a bit of context. It shouldn’t be so surprising that blue light can kill some microorganisms, given that it can harm humans too.
The germicidal flux from the paper is 155.8 mW/cm^2, which is much stronger than sunlight which is about 0.1 mW/cm^2/nm at sea level for short wavelength visible light. I don’t know what your threshold for alarming is, but to me that seems high enough that concern is warranted. And I’m not sure that conventional sunscreen would actually help. Based on this overview of sunscreen, it looks like most broad spectrum sunscreens don’t do much above 380 nm or so.
Also, It doesn’t seem clear to me that the fact that blue light is visible implies it’s not harmful. (UV is harmful, and some species of bird and rodent can see ultraviolet light, as can some humans.) What’s your reasoning? It is definitively known that UVA light is carcinogenic by an indirect oxidative stress mechanism, and I can’t find any discussion of at what wavelength exactly this mechanism stops being relevant. Because the mechanism for germicidal action for 405 nm light (described in the linked paper) is also oxidative stress, it seems very likely that 405 nm light is carcinogenic for exactly the same reason as UVA, although possibly less so.
If your flux is 1,558 times that of sunlight, that’s definitely alarming. At that point, the wavelength might not matter very much; you might be dumping enough energy to sterilize surfaces by heating.
The paper indicates that the treatment generally works by stimulating porphyrins in bacteria or fungi of interest. Humans can have light sensitivity due to porphyrins, a condition called porphyria, but it’s fairly rare. Unless the novel coronavirus has porphyrins in its chemistry, I wouldn’t expect to this effect on the virus, as the paper notes. The reported data indicate that the effect is dependent on other elements of the mixture; something else in the solution may break down under the flux and attack the virus.
My reasoning was basically similar to this sentence from the paper: An alternative mechanism of inactivation when FCV is suspended in MM may be associated with the LED emission spectrum extending slightly into the UVA region, meaning the virus is exposed to very low-level UVA photons (~390 nm).
To be clear, those two units are different. 155.8 mW/cm^2, and 0.1 mW/cm^2/nm. So it’s not 1,558 times stronger than sunlight overall. Neglecting atmospheric effects, sunlight across all wavelengths is 135 mW/cm^2, so about the same total flux—it’s like we compressed the broad spectrum of sunlight to all be a single wavelength. My point is that it’s much much more blue-violet light (not much much more light total) than what we usually encounter. Blue-violet from sunlight may be safe for our skin, but that doesn’t necessarily imply that blue-violet light at germicidal intensity is safe.
This is an important point. Germicidal blue-violet would likely be ineffective against airborne viruses.
This is exactly my concern. What’s to say that the reactive chemical species that “attack” the virus won’t also be a problem for human cells? The mixture in which blue-violet light is more effective was made of “artificial saliva, artificial faeces and blood plasma,” so whatever is breaking down could break down exactly the same way in our bodies.
(To be clear, I’m not saying it’s necessarily unsafe for human skin. I’m just saying we shouldn’t assume it is safe.)