[HN Gopher] Far-UVC light: A tool to control the spread of airbo...
___________________________________________________________________
Far-UVC light: A tool to control the spread of airborne-mediated
microbial
Author : gjvc
Score : 80 points
Date : 2022-01-09 15:28 UTC (7 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| tagoregrtst wrote:
| "[...] far-UVC light cannot penetrate even the outer (non living)
| layers of human skin or eye; "
|
| Without reading their previous reference, this doesn't make
| sense. If it doesn't reach the outer layers, what's blocking the
| light?
|
| Also, I seriously doubt this wont cause cataracts in the long
| term.
|
| By Wiki, light < 200 nm is absorbed by O2. The light proposed by
| the authors is 207< \lambda < 222, so about as energetic as UV
| can be and not be blocked by the atmosphere. Ill take their word
| that it cant make it past the layer of dead skin.
|
| But what protects the cornea? Just the very thin layer of tears?
|
| Turn up the HVAC air exchange rate please! There are many other
| benefits to that.
| causality0 wrote:
| The very careful wording makes me somewhat suspicious. For
| example, they focus on the skin safety of far-UVC, but what about
| long term effects on the cornea?
| geoduck14 wrote:
| Skin safety was a common concern for conventional UVC, and far-
| UVC has been anticipated to solve this problem so it is focused
| here.
|
| They are saying the light waves can't penetrate the fist layer
| of skin... which presumably includes the first layer of eye-
| ball skin. If true, there shouldn't be any impact to the cornea
| over time
| causality0 wrote:
| All their citations have to do with skin penetration. The one
| that even mentioned the cornea only did so in reference the
| amount of UVC reaching the lens. These authors make claims
| which, while possibly true, are not found in their cited
| literature. For example, they say far UVC cannot penetrate
| the tear layer. Their citation doesn't say that. The citation
| says it's unlikely to damage human cells between 10 and 25
| micrometers in diameter. The tear layer averages three
| micrometers in thickness, and it does not contain the
| absorptive proteins responsible for the shallow flesh
| penetration depth. This is shoddy science.
|
| Chronic exposure to 240nm light causes keratopathies. 222nm
| is not 240nm of course but I would demand a better study
| before I agreed to 40+ hours a week of exposure to far-UVC.
| tranzudao wrote:
| I think this is an oversimplification. The cornea differs
| quite a bit from skin histologically. Even if light does stop
| at the first layer of the cornea - the question is how? The
| problem typically found with UV wavelengths is opacification
| of the cornea/lens (cataracts). I have no idea if this is the
| case for the specific wavelength in the paper - but it's
| definitely worth more discussion
| potiuper wrote:
| The article links to
| https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC5552051/ that
| states "Therefore, penetration of far-UVC ~200-nm light through
| the cornea to the lens is Predicted to be essentially zero (15)."
| 15 is titled: "UV absorbance of the human cornea in the 240- to
| 400-nm range." Further, the main claim is "in microbes that are
| much smaller in size than human cells [less than 1 mm in
| diameter, compared to the diameter of typical human cells ranging
| from about 10-25 mm], [far UVC] is strongly absorbed by the
| proteins in the cytoplasm of human cells and is drastically
| attenuated before reaching the human cell nucleus" DNA and other
| proteins are known to be more affected by 220 nm due to
| absorption peaks than 254 nm. From
| https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradia... :
| 'Another potential danger is the UV production of ozone, which
| can be harmful when inhaled. Lamps designed to release UV and
| higher frequencies are doped so that any UV light below 254 nm
| wavelengths will not be released, to minimize ozone production.'
| The lights are most applicable placed at the at the coils and
| drain pans of cooling systems as 'forced air systems by design
| impede line-of-sight, thus creating areas of the environment that
| will be shaded from the UV light.'
| https://pubmed.ncbi.nlm.nih.gov/28941399/ concluded 280 nm worked
| better than 265 nm for water disinfection.
| fsh wrote:
| All deep UV wavelengths are energetic enough to break chemical
| bonds and the cross sections have quite non-trivial wavelength
| dependences. The authors of the article claim that 222 nm has a
| much shorter absorption length in tissue than 254 nm. This
| would drastically reduce the intensity that can reach the
| living cells under the outer layers of the skin.
| 1-6 wrote:
| Bacteria is a lot more difficult to kill because of the size.
| This is great for viruses though. I've always wondered about the
| effectiveness of UVC, humidity, and ozone for the control of
| COVID.
| gene-h wrote:
| If this does indeed take off, we may expect the next trend in
| fashion to be clothing with with stripes and other features that
| fluoresce under said UVC light.
| bratwurst3000 wrote:
| Seems like a way to risky idea... gut feeling. And there are
| problems. First the uv has to reach the virus. If there are
| shadows its over. Its super hard to ilumate a room perfektly....
| And may i propose an alternative. Use a hepa filter that changes
| the air in the room at a rate that would make in impossible to
| have much virus in the air... also not that easy but imho way
| safer than UVC
| radu_floricica wrote:
| How many ways I hate your comment? let me count the ways.
|
| 1. Somebody comes with a potentially awesome idea, you have a
| gut feeling it's risky, and start looking for confirmations of
| your gut feeling. Way to #hit on somebody else's initiative.
|
| 2. "The virus" (we all know we aren't talking about
| tuberculosis here) is airborne, which means it'll float around.
| If there are shadows it's not "over", it what scenario it would
| even mean anything for shadows to be game over? An
| instantaneous flash once?
|
| 3. An alternative is not an argument. Hepa filters work, and I
| completely agree that we should be using them a lot more but:
|
| 3.1 We aren't using them a lot more, so for some reason they
| don't fix the problem, so alternate solutions are very welcome
|
| 3.2 There's room for more than one took in a toolkit, for
| reasons too obvious to get into.
|
| ----------------
|
| Now why am I taking the time to write a comment 5x the length
| of yours? Because you're merely doing in a somewhat more
| obvious and inexperienced way what society has been doing
| for... at least a couple dozen years. Anything new is risky, we
| should carefully study side effects and only when it's clear
| there aren't any we're allowed to move forward. This is
| especially true for medical tech, but it's part of a larger
| disease that's in the same constellation with NIMBY, regulatory
| capture and taxi medallions being worth a million.
|
| Covid made it obvious that a lot of emperors didn't wear
| clothes. We could have had mRNA vaccines quite a bit earlier -
| and I'm sure the companies involved would have been perfectly
| happy to make money from them. But no, there had to be a
| pandemic for regulatory agencies to even consider approving
| such new tech.
|
| We could have had WFH ten years ago, the tech was here. It took
| barely weeks for IT departments and worflows to adapt. But no,
| managers had to negotiate in the strictest terms for even one
| day a week of WFH, because it's Something That Is Not Done.
|
| And you have a gut feeling that it's risky tech, and I get
| triggered.
| bratwurst3000 wrote:
| Dude first I didnt want to trigger you and I apreciate your
| comment. But isnt saying its a gut feeling somehow
| communicating it is understood that this isnt the standpoint
| of a scientist? Thats mostly common sense. So why go into
| ragemod on sth I did state as something not to take
| seriously?
|
| But you made a long comment so I will take the time to engage
| with you.
|
| 1. a potential awesome idea it isnt. Uvc is very strong and
| every layman should now that it can kill bacteria and viruses
| ... it can even split chemical bonds. And a it should be
| known that it creates ozon and could cause cancer. But this
| is a question of the intensity. And also as the ozon layer
| filters uvc we dont have much contact. But it is safe to
| asume that if UVA and UVB are causing cancer so should UVC
| ... the next lvl of higher energy is X-ray and gamma and
| beta. Funny stuff
|
| 2. a scenario where to people are talking to each other and
| the uv cant radiate between them.
|
| 3 I did propose the hepa filter because the problem is the
| following. You have a rate of virus getting in the air and a
| rate it is killed by uv light and a rate of it is absorbed by
| the hepa filter. So imho a room were air can circulate easily
| there should be a possibility of getting to the rate that the
| air in the room is changed sufficent quickly to not get
| anough virus to make people ill. UV light is a good choice
| and allready used in hospitals and cheap. But when nobody is
| there. But i still dont think its a good idea to throw high
| energy radiation onto people just to be safe.
|
| 3.1 they are expensiv and getting to a solution is not what
| this society is made for
|
| 3.2 i totaly agree with you and every option should be
| validated.
|
| But do I have the right to an opinion? I dont want to disrupt
| the discussion about potentialy helping ideas. But when
| someone stats a doubt it would be nice to answer polite and
| engaging on the doubt.
|
| And I understand you have a history that made you get
| triggered but dude ... I am not part of that history. Wish
| you the best
|
| Edit: ar last i want to state that the succes of a medicine
| to finish phase three is like 1-5% ... so good that we have
| those mechanics to prevent harm to society... but this is a
| old discusion
| radu_floricica wrote:
| Yeah, should have made it more clear that it's not
| personal.
|
| But look at the other comments. Look at what zarzavat is
| saying below. "The burden is on the inventor" - and since
| he mentions microplastics, I'm allowed to assume he's
| talking about high levels of certainty and second order
| effects.
|
| This has never been true in the whole human history. Ever.
|
| This itself, this "being certain every innovation is 100%
| harmless" is a huge departure from how things have been
| done, and in itself has a huge risk. I'm not talking about
| not having shiny new cool stuff, or not having a colony on
| Mars. I'm talking about apples and apples - about this kind
| of meta-strategies just plain costing more lives than they
| save. Google "FDA delenda est", for smarter people than me
| saying that FDA was _way_ too conservative in the pandemic.
|
| Somebody said below that I'm mistaken about regulatory
| agencies delaying mRNA before the pandemic. We could of
| course try and get into the gritty details about what they
| delayed and why, but just consider one thing: Moderna had
| their covid vaccine ready in a matter of WEEKS. And it's
| the same vaccine we're using now. I don't know without
| googling when Pfizer had their first version, but I imagine
| it's around the same timeframe. Does this sound like
| immature technology? When two companies immediately come up
| with a vaccine when really needed?
|
| What is more likely, that it somehow happened right now for
| god knows what reason, or that they were both ready to use
| mRNA but couldn't?
|
| And people keep dying around us. Of Covid, of cancer, of
| dozen of diseases, not to mention plain old age. This is
| not about micro-plastics - it's lives vs lives. We have
| (all around the world) a much more conservative system than
| we need.
| bratwurst3000 wrote:
| That I can partly sign. The complexity is way out of
| controll and it is way to hard to get stuff done with all
| regulation. But somehow we need regulations. So where is
| the golden way? If we overregulate people will shout that
| potentialy beneficial things wont happen.... On the other
| side if we dont regulate people could be killed with
| harmfull stuff that could be prevented.
|
| Honestly this question is puzzling me since a while and I
| cant even state a direction I would take because its to
| complex for me..... but gut feeling says more
| transparancy and less complexity could work in designated
| areas... but ... gut feeling.
|
| And as said I understand your first rage. With the past
| years we are all on the edge with strangers, me too. And
| I did somehow mumble a bit ...
|
| Edit: to the vaccine part. It seems easy to develop them.
| A friend working at a well known biotech lab was even
| thinking about making one on the fast way for himself.
| The hard part is to scale the production and have a good
| one. As far as I remember those two werent the only
| ones... but those that worked well. But at first I was
| rly impressed that they got it that fast and then I was
| even more impressed about the scalling problem. My friend
| told me about it and it was fascinating.
| cowsandmilk wrote:
| > there had to be a pandemic for regulatory agencies to even
| consider approving such new tech.
|
| That's nonsense. There were no regulatory agencies blocking
| mRNA vaccines. There has been a path towards their approval
| for a long time. And products such as EndeavorRx, a therapy
| delivered as a video game, show that FDA is willing to create
| paths for novel types of therapies in recent years.
| radu_floricica wrote:
| > There has been a path towards their approval for a long
| time.
|
| QED
| zarzavat wrote:
| Between the forever chemicals, microplastics and air
| pollution we already have quite enough "good ideas" trying to
| kill us. The burden of proof for any potentially hazardous
| new invention is on the inventor to prove that it is safe.
|
| People who are dismissive of new ideas based on safety
| grounds don't need to provide reasoning or evidence or even a
| coherent argument, they provide a useful function nonetheless
| by adding friction, forcing inventors to prove that their
| invention is safe beyond doubt. Since this idea proposes
| using ionizing radiation around people, a strong dose of
| scepticism is warranted.
| musingsole wrote:
| Eh, not techy and sparkly enough. It won't convince the
| laypeople that they're safe enough if the only palpable aspect
| of the system is a slight breeze.
| abecedarius wrote:
| As kind of an echo of radu_floricica's comment upthread:
| dismissing some X because some other people allegedly will
| have unreasonable concerns, that's another disease of
| discourse we get too much of. I wish people would restrain
| themselves from bringing up that kind of alleged obstacle
| until after getting to some kind of rough consensus at the
| object level.
|
| It's like a recipe for "We can't ever improve anything
| unless, somehow, magically, there's already common knowledge
| of the fix." The object-level talk is necessary to getting to
| common knowledge!
| savant_penguin wrote:
| Wow now this is a convincing result
|
| https://media.springernature.com/full/springer-static/image/...
| mackatsol wrote:
| Ok, I'm convinced. So how / where can I find such a light to use
| in our apartment lobby (for example)?
| giarc wrote:
| If you search my username in this thread, you'll see another
| comment by myself. I can't remember the product name, but there
| exists a company that makes a UV light system that swaps out
| for the usual fluorescent light you see in most commercial
| buildings. I'm not affiliated with the company at all.
| bluGill wrote:
| I'd go for a HEPA air filter instead, some also have UV light
| inside
| jcims wrote:
| Pretty interesting video demonstrating UV (not sure what part of
| the spectrum) killing microbes.
|
| https://youtu.be/sJVtNsezGUI
|
| Really a great channel, some of the best microphotography out
| there.
| 41b696ef1113 wrote:
| Is it standard practice for commercial HVAC to have some kind of
| UV light/ozone/X pathogen killing mechanism somewhere in the
| ducts? Or would that only be installed on a HEPA style system
| going for a certified clean environment?
|
| I would naively think that exposing the forced airflow to the
| treatment would be both simpler and safer than installing a
| system into every room with people.
| giarc wrote:
| I work in this field (infection control) and see a lot of
| products being pushed, especially lately.
|
| One we actually installed in our hospital is a replacement for
| the regular fluorescent lights you see in every building. It's
| a direct swap out so pretty easy for any maintenance crew to
| complete. Instead of directing the UV light into the room, it
| simply has a duct inside with a fan that directs air to pass by
| powerful UV lights. The UV light is contained to a small box
| within the unit and the people around never are exposed. The
| only drawback is the fan noise, but in hospitals, the
| background sound is already pretty high. I believe you can
| schedule the fan to stop overnight. Otherwise it basically
| continuously circulates the air in the room, always passing
| over a UV source to kill pathogens that might be in the air.
|
| EDIT - just to clarify, you swap out the whole box, not just
| the bulb. Like this (http://2.bp.blogspot.com/-etoHnNVcOnw/Tu0x
| Y9sDwCI/AAAAAAAAA3...) but usually in a drop ceiling.
| DannyBee wrote:
| It's not standard because you can just use filters.
|
| Keep in mind the filters have to be able to filter the dead
| pathogens anyway (usually same size) or else you are breathing
| them, which isn't great either. Better than live ones for sure,
| but not great.
|
| As for UV, you can add it to either residential or commercial
| easily (some preschools and schools I've visited added them in
| the past year). It doesn't make sense to install in every room,
| as you say.
|
| On ozone, see https://www.epa.gov/coronavirus/air-cleaners-
| hvac-filters-an... and the section on ozone.
| cipheredStones wrote:
| What's the risk from dead pathogens - immune overreaction?
|
| It's a screwball idea, but I wonder if there might actually
| be health _benefits_ to reliably killing pathogens without
| filtering them out of the air - sort of like low-dose
| inactivated-agent vaccines for everything you would have
| actually been exposed to otherwise.
| JulianMorrison wrote:
| That would treat the ducted air but it wouldn't treat the air
| already in the room. And if the air is being recycled, it would
| still linger for some bounded time before being pumped back
| through treatment.
|
| Having the UV in the room with the people means it treats every
| breath immediately.
| DannyBee wrote:
| It's not quite that simple - the lingering also depends on
| particle size (ie is it in a droplet, or bare, or ...)
|
| Most places with lots of people also have very high acph -
| often 20-30 air changes per hour.
| rapjr9 wrote:
| It does sound as they say "promising" but when do they do the
| big, decades long double blind, randomized, controlled study of
| long term effects? What if you have a wound in your skin, does it
| become cancerous because the live cells are exposed to far UVC
| light? What does it do to plastics? Do humans get sick easier if
| they are living in a sterile environment? Does it kill plants?
| Far UVC is not a natural phenomena on Earth.
| SideburnsOfDoom wrote:
| As I understand it, the usual design of systems that use UV
| light to kill viruses do not simply shine it into the room like
| a ceiling light; rather there's a box with a UV light in it,
| and a fan to draw air through that box.
| pfyy wrote:
| I have a question. Does anybody know why we keep our indoor light
| sources uva / uvb free ? I know that too much UVA/B light seems
| to be carciogenic, but a small amount of it, especially UVB seems
| to be beneficial to human and still kills germs, especially covid
| [1]
|
| The positive effects are a) vitamin d production b) germicide
|
| The negative effects are c) lower energy efficiency in the
| visible spectrum (watt per visible light produced) d) negative
| effect on the eye e) carciogenic
|
| For indoor keeping of reptiles UVB light seems to be needed [2]
| As far as i've read, for indoor planting, UV light seems to
| beneficial as well, for example it increases the production of
| THC [3]
|
| Why should we, as humans, be different ?
|
| [1]Ratnesar-shumate, S.; Williams, G.; Green, B.; Krause, M.;
| Holland, B.; Wood, S.; Bohannon, J.; Boydston, J.; Freeburger,
| D.; Hooper, I.; Beck, K.; Yeager, J.; Altamura, L. A.; Biryukov,
| J.; Yolitz, J.; Schuit, M.; Wahl, V.; Hevey, M.; Dabisch, P.
| Simulated Sunlight Rapidly Inactivates SARS-CoV-2 on Surfaces. J.
| Infect. Dis. 2020, 222 (2), 214-222.Google Scholar https://sci-
| hub.st/https://doi.org/10.1093/infdis/jiaa274
|
| [2] https://en.wikipedia.org/wiki/Ultraviolet#UVB
|
| [3] https://vanessa-nielsen.com/cannabis-plants-uv-light/
| weaksauce wrote:
| if i had to guess there are a few reasons they don't do this...
|
| the first and most important reason is manufacturers have and
| will optimize for the main benefit of a product. the main
| product here is light. heat came as a negative byproduct of
| traditional incandescent lights and heat is something to
| minimize to lengthen the life of an led bulb.
|
| another possibility is that if it were widespread it could
| cause some negative outcomes of people sitting too closely to a
| source of it and potentially exposing the companies to legal
| issues. not a lawyer and they might be able to shield
| themselves from that liability with well written disclaimers
| though.
|
| Along with inertia from the incandescent bulbs not emitting
| that wavelength... the most likely reason is that they don't
| want to spend the money on researching how safe it is and how
| to cost effectively make them like that though.
| defaultname wrote:
| UV A/B is oxidizing, which is why plastics left outside degrade
| rapidly, discoloration occurs, etc. It's bad for your eyes, bad
| for your skin in excess, and creates ozone in the air which is
| an environmental pollutant.
|
| Normal indoor plants have no need for UV at all. Nor do most
| food plants -- greenhouse glass blocks UV, for instance.
| collegeburner wrote:
| Because UV fades fabric, degrades plastic, damages and
| discolors wood, etc.
| briHass wrote:
| CFL bulbs, especially earlier versions often emitted a
| surprising amount of UV light. The speculation is that the
| tight coils of glass would result in breaks in the phosphor
| coating, letting the UV through.
|
| I know I have fixtures that used to have CFLs in them, and any
| plastic is yellowed significantly.
| sega_sai wrote:
| I don't think germicide is necessarily good. There are theories
| that the abundance of allergies and autoimmune diseases is
| partially caused by excessive cleanliness/lack of exposure to
| microbes etc.
| scotty79 wrote:
| I think allergies and autoimmune diseases are partially
| caused by the fact that people are no longer work infested
| with parasites in yhe way they were all the time since
| forever. Parasites suppress immune responses.
|
| I think we should figure out how to substitute their
| influence on humans before we conclude that exposing
| ourselves to bacteria and viruses a lot is a good thing.
| ozfive wrote:
| Where can I buy one?
| ISL wrote:
| The article has an interesting changelog in the Competing-
| Interests section, which led to this correction:
| https://www.nature.com/articles/s41598-021-97682-w
| geoduck14 wrote:
| 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
| aaaaaaaaaaab wrote:
| >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 wrote:
| You can say the same thing without being mean.
| baskethead wrote:
| 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 wrote:
| > _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 wrote:
| 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.
| bratwurst3000 wrote:
| 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.
| CryptoPunk wrote:
| >>of the limitations on both is the shadow effect... got to go.
| I'll elaborate if there is interest
|
| Yes please
| rapjr9 wrote:
| 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-
| rest...
| 323 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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-...
| fsh wrote:
| 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.
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