Further Research on 222nm far UVC light as Safe

I have to listen very intently to understand any British accent, but this was worth the effort!

I wish he had spent a little more time on his last point regarding exposure of the upper layer of air in a room to longer wavelength UVC. Having had a very painful personal experience with reflected 254nm UV, I'm very concerned abut reflected and refracted radiation from such a system.

It definitely sounds like 222 is something of a magic number!

Well it seems the shorter the wavelength the less penetration, now below 180nm the wavelength won't even penetrate the air, at 222nm just the top layer of skin cells, 254nm penetration well below the upper skin layer, and so on....the 180nm creates ozone by splitting molecules in the air...the eyes are protected by the thin layer of moisture that coats the eyeball...it seems that even with prolonged exposure the 222nm wavelength can't penetrate any further than the very top layer of whatever is exposed....So the light needs to be concentrated at the 222nm wavelength and have any other wavelengths that the light is producing blocked by a filter....there is no absolutely pure source of 222nm wavelength light that I know of...yet.... without blockers...

Arrange the Space Zen

dkwarner, SE, or anyone else,

I know this is very likely a superficial question but...
I did some puttering around the periodic table and....
Eximer laser wavelengths look like this..

Go higher in the noble gasses and your wavelength increases.
Go higher in the halogens and your wavelength decreases.

I see that Ushio has the 222nm filtered KrCl eximer for UVC generation.
I wonder if anyone has come at the problem of generating far UVC from
the other direction ? For example, KrBr at λ=207 nm. Specifically....

1) Do you know if the 207nm is close enough to get the sterilizing effects
seen at 222nm ?
2) Are KrBr eximers too inefficient or too costly compared to KrCl ?
3) Does air ionize too easily and suck the power out of the beam ?
4) Does a KrBr eximer produce spurious wavelengths which are a big problem ?
5) Is there some other problem making KrBr less viable than KrCl ?

Below find a sample of references I used to navigate eximers and
arrive at these questions. Note the last reference also refers to the KrBr as narrow band

which might reduce or eliminate filtering.

_____________
thewildotter

https://www.gigaphoton.com/en/technology/laser/what-is-an-excimer-laser
An excimer laser is an ultraviolet (UV) laser that uses a compound of noble gases,
halogen, etc. as its laser medium, typical examples being
ArF excimer lasers (wavelength of 193 nm),
KrF excimer lasers (wavelength of 248 nm),
XeCl excimer lasers (wavelength of 308 nm),
and XeF excimer lasers (wavelength of 351 nm).

https://www.ushio.com/product/care222-filtered-far-uv-c-excimer-lamp-module

The low lying excited electronic state of the Xe atom generated by
the e-beam reacts with Br2 to produce XeBr* which undergoes a
bound-free transition with a wavelength of 281.8 nm.

A dielectric barrier discharge in mixtures of xenon and iodine to
provide intense narrow band ultraviolet (UV) radiation at λ = 253 nm
(XeI∗) has been investigated.

An excimer lamp (or excilamp) is a source of ultraviolet
light produced by spontaneous ... KrI*, 190,

https://www.researchgate.net/publication
/231059302_Investigation_of_excimer_ultraviolet_sources_from_
dielectric_barrier_discharge_in_krypton_and_halogen_mixtures
The characteristics of the emission spectra of Kr/Br2 and Kr/I2 mixtures
driven by dielectric barrier discharge as a function of gas pressure
were respectively investigated. It was found that the KrBr* excimer lamp
provided an intense narrow band ultraviolet (UV) radiation at λ=207 nm,
whose intensity was strongly influenced by gas pressure and buffer gas.
The excimer radiation at λ=191 nm generated by the KrI* excimer lamp was
very weak and less dependent on gas pressure due to predissociation which
was confirmed by the strong emission of the atomic iodine line at λ=183 nm.

https://www.ledinside.com/news/2015/7/columbia_university_and_ushio_enter_exclusive_uv_lighting_technology_license_and_research_agreement

They make both....why 222 was chosen over 207nm eludes me at present, but I'm assuming there's a good reason...I'm guessing that the 222nm wavelength is more effective....sort of like comparing a .25 cal bullet with a .32 cal bullet...goes a little deeper but still no collateral damage...

Marketing Evil or Normal Tech Advancement ? Machts Nichts: Twist and Shout

Call me a cynic but my first suspicion is a phased marketing plan... " We have all these filters that we would like to unload at a high markup. As long as we have little competition, lets sell the laser that needs our premium filters instead of the one that would work safely with no or cheaper filters. As soon as someone else starts to compete with our high profit model we can release our better/cheaper one and maintain market dominance. "

Decades of watching such predation from the corporate insides leads me to guess that ahead of honest "physical reality" motivations. I have no specific reason to suspect Ushio of such intent other than it is a corporation with global sales. At any rate, if the questions get asked then the move to phase 2 of the marketing plan is often accelerated. That is my motivation for thinking with paranoia about any problem which seems, for the moment, to (red flag) only have expensive answers. Even if only the genuine physical reality motivators exist, a little perturbation of the space often shakes out better/cheaper answers. So, machts nichts ("it makes no difference.") Progress gets achieved by shaking up the current solutions (see simulated annealing theory) regardless of commercial morality issues. Twist and shout !

I want the darned lights, I want them now, and I don't have a truckload of money for them. I have some of the 254nm Hg ones already but I would prefer these inherently safer ones which are, as things stand, out of reach.

______________

thewildotter

I've read/heard so many articles/papers on this recently that I can't keep track of which said what, but I think it was the YouTube video of your 2/21 post that said that UV radiation below 200nm was absorbed by air, and was referred to as Vacuum UV. I don't recall seeing/hearing any values for distance travelled before X% reduction in intensity.

I'm clearly no expert, but I expect there to be a gradual variation in absorption with wavelength, so the 207nm may not travel far enough in air for it to be effective for disinfecting large areas.

Also, the disinfection appears to depend on breaking molecular bonds. If any resonance is involved in breaking those bonds, then there will be an optimum wavelength, and 207nm might be too far from that optimum. There is a much larger gap between 222 and 254nm (also known to disinfect) than between 207 and 222nm, so I doubt if this is a major factor.

Short Air Travel Can be a Feature

dkwarner, Good thinking. Sometimes these observations cut both ways. For example one could potentially disinfect the bulk of the air in a convention hall or sports arena with lights pointed at the ceiling and measure only a tiny fraction of their radiant intensity where the people actually are. Thus social distancing in a KrBr lit stadium might be effective at say 25% occupancy as opposed to 3% occupancy otherwise. In the cases of interest for me, an HVAC installation would not need to be light leak free since paths beyond the ducting would be attenuated by simple distance. Also, wand disinfecting would not need to be so compulsively reflection and nearby co-worker conscious. For wound disinfection, longer exposure times might mean better disinfection despite less penetration into tissues since shorter wavelengths for shorter penetration seem to be key to a lot of 222nm claims of safety relative to 254nm. The saline water film on your cornea may stop 207nm wavelengths in an even shorter distance than it stops 222nm light. All of this would, of course, need measurement and experimentation for verification. I am very interested to see the KrBr lamp spectral distribution to see how it compares to KrCl with and without a filter.

______________

thewildotter

Excellent answers! Thanks!

Now, if you can find a similar graph regarding UV absorption/penetration through air at room temperature, that would be really GREAT!

https://www.osti.gov/servlets/purl/810964

https://www.lesswrong.com/posts/3yCcdg7DQQnfqZoax/far-ultraviolet-light-in-public-spaces-to-fight-pandemic-is

Looks from this graph that they might not have really gotten outside of all the atmosphere for some of their data. Blackbody separating from "sunlight above atmosphere" is suspicious.

___________

thewildotter

Another interesting, although not unexpected thing in your ARTI-21CR/610-40030-01 reference as well as your graphic is that they show the germicadal[sic] range extending from UVC all the way through VUV into x-ray. Clearly, they knew that those energies are enough to blast DNA. By continuity they should have included 200nm down to the 232nm(oops, I incorrectly said 242nm before) inflection point. None of this is to criticize your providing the data, SE. I appreciate your efforts and talents. I also appreciate your evangelism for new/better/safer sterilization tech.

_____________

thewildotter

The Interesting Stuff is Usually on the Edges

Early work established 220 to 300nm with a peak at 265. So, it appears that over the range they were looking at back then they missed the inflection point at 242nm or simply had no way of going below 220nm convenient to their work. Maybe this inertia has cause them to ignore shorter wavelengths of UVC ever since for purposes of sterilization. That plus the fact that the next band is called "vacuum uv" because of the short travel distance in air may have dissuaded them from looking down to 200nm. And there lies this jewel. I am still lacking a quantified travel distance in this interesting range. Did I somehow miss it in your reference ?

__________

thewildotter

per: https://www.osti.gov/servlets/purl/810964

================================

11.0 INTRODUCTION 1.1 Background The use of ultraviolet (UV) lights to disinfect room air and air streams dates to about 1900. Richard Riley has numerous publications in the 1960’s and 1970’s that deal with UV disinfection and has published an extensive review (Riley, 1988), as has Shechmeister (1991). Early work established that the most effective UV light wavelength was the wavelength range from 220 to 300 nanometers (nm), with the peak effectiveness near 265 nm.

https://www.ushio.eu/excimer-explained/

Light irradiance is a function of the inverse square law, so you figure the level of irradiance, the temperature/density of the air, the humidity and other particulate present....

https://www.intl-lighttech.com/inverse-square-law-light-calculator#:~:text=The%20inverse%20square%20law%20of,the%20square%20of%20the%20distance.

Yep. I agree, there are lots of details the devil often inhabits. I also like that this is an HVAC setting, about which I have interest.

___________

thewildotter

...and is subject to Rayleigh scattering...

https://www.britannica.com/science/Rayleigh-scattering

"A portion of the incoming solar radiation is absorbed by gases in the Earth's atmosphere. These gases absorb electromagnetic energy at certain wavelengths, therefore in certain portions of the electromagnetic spectrum very little energy is absorbed (for example the visible) while in other portions like the Ultraviolet, nearly all incoming energy is absorbed. The portions of the spectrum that are absorbed by atmospheric gases are known as absorption bands."

http://gsp.humboldt.edu/OLM/Courses/GSP_216_Online/lesson2-1/atmosphere.html

Excellent Data !

Wow ! This looks even better for KrBr than I was expecting. First realize that on the DNA plot the XeBr #4 is irrelevant for our KrBr vs KrCl discussion. The DNA curve #1 in this graph is, on the other hand, very pertinent. If you overlay the first plot onto the DNA plot with the peak intensity intersecting the DNA plot at 207nm we are near the top of effectiveness for killing DNA. The extraneous radiation away from 207nm from the first plot is not nearly as bad as the KrBr_KrCl excilamp extraneous radiation. The filtered KrBr looks really good, not unlike the filtered KrCl but the point of DNA intersection is better. There may be a double edged sword here in that 207nm is soooo good at killing DNA that while we may be blasting viruses and such, even a tiny amount which might sneak through is very dangerous. For "DNA", including the human DNA it might somehow reach, it looks to be around twice as deadly as 222nm so the moisture and dead skin protecting us had better do a very good job.

The fact that they did not choose to promote KrBr must mean that we are still missing something. I admit that the "something" might be some physical reality item but so far I do not perceive it. Thanks SE, for your data. You always amaze me (GA) with how you find such on-point info.

______________

thewildotter

..." The band gap of aluminium nitride (AlN), meanwhile, is about 6.4 eV, corresponding to a natural emission very deep in the UVC, at 210 nm. As a result, Al-GaN LEDs emit light at wavelengths somewhere in between, depending roughly on the ratio of aluminium to gallium.

Far-UVC LEDs based on such alloys have already been demonstrated in the lab. Since 2007, for instance, Hideki Hirayama at the Riken research institute in Saitama, Japan, and colleagues have been creating Al-GaN LEDs with emission wavelengths down to 222 nm (Electr. Commun. Jpn 10.1002/ecj.11667). Meanwhile, with an emission at 210 nm, the shortest-wavelength UVC LED was demonstrated in 2006 by Yoshitaka Taniyasu and colleagues at the NTT Basic Research Laboratories in Atsugi, Japan, based on pure AlN (Nature 441 325).

Unfortunately, these lab devices have an efficiency of barely a few per cent – well below the 20–40% needed for practical use – which means that none of them has ever been commercialized."....

https://physicsworld.com/a/the-potential-of-far-ultraviolet-light-for-the-next-pandemic/

The 222nm far uvc light is not totally safe for human, we are in uv industry, it is researched that people are not allowed to receive 22mj/day.

Links? Citations?

These findings are based on the latest research....we have found that existing standards were based on speculation rather than fact when dealing with the 222nm area of uvc light...I have provided information on this for the past year or so and have many threads in this forum listing research done in this field...If you take the time to read these research findings I'm sure you will agree...It's relatively new technology and is not widely known, at least in the beginning it wasn't....probably a little more widely known know...