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My question was: "Why does it block UVB?". Found the answer on Quora: https://www.quora.com/Why-does-glass-block-UV https://www.quora.com/Why-does-glass-block-
by pasta 8y ago
My question was: "Why does it block UVB?".
Found the answer on Quora: https://www.quora.com/Why-does-glass-block-UV https://www.quora.com/Why-does-glass-block-UV
"With a band gap of 4eV, glass can't absorb any photons with less energy than UVB light; namely, it is transparent to UVA, visible light, infared, etc; but the higher energy photons can and are highly likely to be absorbed."
So it seems hard to create glass that doesn't block UVB.
- Etheryte 8y agoQuartz glass is transparent to the UV range, so it's not so much that we don't have the technology, it's just way more expensive than regular glass.
- masklinn 8y agoSapphire's also transparent down to far ultraviolet (150nm). Not sure about ALON.
- masklinn 8y agoReplying to self (because the edit window has gone): ALON apparently goes down to 200nm, so it's transparent to UVB (280-315)
- Florin_Andrei 8y agoSapphire is an incredibly trivial compound, aluminum oxide. The problem is, its melting point is huge. To make artificial sapphire you have to melt the stuff at very high temperature and let it drop and collect onto a ceramic base or something. And then you cut, grind and polish it into shape, which is not easy either because it's an extremely hard material. The challenges to making a large flat plate of AlOx would be huge.
- vanderZwan 8y agoYou can coat it - sunglasses are, for example. The coating can be invisible to the naked eye too, I think. This is one of those situations where I think government intervention is needed. I bet the long-term benefits of coating glass like this are very real - both for society and individually (especially in professions that involve a lot of driving time). However, the short-term economic incentives work against it - there is probably a strong first-move disadvantage. Also, what is the economic benefit to a landlord to have UV-proofed glass for their tenants? But if government were to implement a policy of requiring glass in cars and buildings to be coated like that? That levels the playing field. I doubt it is going to happen any time soon though. But of we were ever going to to do that, I know for a fact that are also coatings with reflective layers (invisible to us) that tell birds that the glass is there, which would also save a lot of wildlife.
- losvedir 8y agoAh, yes the classic "government intervention to attack a misunderstood problem with a solution that won't work".
- vanderZwan 8y agoAh yes, the classic "I just assert that governments can only intervene with wrong solutions, without in any way engaging with the topic at hand and actually arguing why it is a wrong solution."
- kortilla 8y agoWell it’s a wrong solution since glass already filters it. Seems a bit premature to salivate over regulation for something that isn’t a problem.
- vanderZwan 8y agoDid you read the other comments? I misread GP and the coating I talked about is for UVA radiation.
- georgyo 8y agoHow does coating it prevent the glass itself absorbing UVB?
- vanderZwan 8y agoAs Waterluvian pointed out, I misread GP and explained how we could make glass block UVA as well.
- Waterluvian 8y agoI think you're inverting what parent is saying. Glass by nature seems to block UVB.
- 8y ago
- spuz 8y agoThere's a great Applied Science video on the various light absorption properties for various materials here: https://www.youtube.com/watch?v=vwsHRrDYu5o https://www.youtube.com/watch?v=vwsHRrDYu5o
- harperlee 8y agoSo in case anyone just panicked thinking “Wait, so do my car and office windows block cancer producing UV or not??”, this is what I found on cancercouncil.com.au (first google result): - UVA penetrates deeply into the skin (the dermis) causing genetic damage to cells, photo-ageing (wrinkling, blotchiness etc) and immune-suppression. - UVB penetrates into the epidermis (top layer of the skin) causing damage to the cells. UVB is responsible for sunburn – a significant risk factor for skin cancer, especially melanoma. Which contrary to what I knew, links melanoma to sunburn, not DNA damage.
- garmaine 8y agoWhy are you assuming there isn’t DNA damage when sunburned?
- logfromblammo 8y agoThe UV damages the DNA. That step is usually required to produce melanoma cancer. The sunburn causes the deeper cells with damaged DNA to multiply in order to replace the damaged cells. A single quiescent skin cell with precancerous DNA can be cleaned up by the immune system. A precancerous cell that has multiplied itself to cover a patch of sunburn, activating some of the genes for rapid growth, is much harder to clean up.
- meschi 8y agoWell, when you get sunburn i.e. high UVB exposure, you get high UVA exposure, too. My understanding is, that UVA radiation causes cancer. But I would like to see some clarification on this topic, too.
- rjf72 8y agoMildly amusing related aside from this. Because of this, glass is completely opaque in the UV spectrum. Looking at the world in UV [1] is quite interesting! Such a reminder that how and what we experience of the world is so largely a product of our physiological composition. What is perfectly transparent to us would be a great hiding place from the perspective of something that only saw in UV. [1] - https://www.youtube.com/watch?v=V9K6gjR07Po https://www.youtube.com/watch?v=V9K6gjR07Po
- deleted 8y ago[deleted]
- hopler 8y agoOther comments say glass does not block UVA
- lightedman 8y agoSoda-lime glass transmits pretty much all UV ranges and is readily manufactured (it is used often in germicidal lamps.)
- kough 8y agoFeynman knew this and claims to be the only person to have watched the Trinity test with naked eyes, rather than through welding goggles: > In Surely You’re Joking, Mr. Feynman, American physicist Richard Feynman speculates that he may have been the only person who watched the Trinity Test relatively directly, using a windshield to exclude ultraviolet light. Everyone else, he claims, was looking through something akin to welding goggles. https://www.sindark.com/2011/02/22/feynman-and-the-trinity-test/ https://www.sindark.com/2011/02/22/feynman-and-the-trinity-t...
- Bartweiss 8y agoI've never really understood this story. Feynman wasn't wrong, but UV-A and even sufficiently-bright visible light also cause eye damage. Did he know the main visual hazard from the bomb was UV-B? Did he just get lucky?
- Spellchamp 8y agoYep, he basically says that he knew the only thing that would damage his eyes would be UV-B, so he just went for it. Long time since I read the book but that's what I remember.
- StrictDabbler 8y agoWe don't even know that he got lucky. Lasers didn't exist yet to force us to study retinal exposure to bright non-UV light and the flash from the bomb didn't last that long, nor were the first few bombs that bright, so he may have been fine... but obviously if you stare at the sun through three inches of glass you're still going to burn your retinas. He says "I figured the only thing that could really hurt your eyes (bright light can never hurt your eyes) is ultraviolet light. I got behind a truck windshield, because the ultraviolet can’t go through glass, so that would be safe, and so I could see the damn thing." What we know from later laser research is that unless you have a comprehensive visual field test, it's often hard to identify that part of your retina has been scorched. Your brain just filters it out as a blind-spot and you don't realize what you're failing to see. There's every chance that Feynman totally burned a section of his retina and never realized it, and there's every chance that he was fine because the exposure at his distance wasn't that bad, but at the end of the day he was more reckless than insightful in this situation.
- devy 8y ago> So it seems hard to create glass that doesn't block UVB. Physics aside, why would you want to do that in the first place? UVB is the chief cause of skin reddening and sunburn and plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. [1] Just for that little benefit of triggering Vitamin D synthesis is not worth the increased risk of skin cancer IMO. And the author lays out the alternative there too: "Those concerned about low vitamin D levels can get more of the vitamin through foods. " [1]: https://www.skincancer.org/prevention/uva-and-uvb https://www.skincancer.org/prevention/uva-and-uvb
- tlals 8y agoThere is an alternative view that regular sun exposure is beneficial, and that many of the health benefits linked to vitamin D are actually just using vitamin D as a proxy for sun exposure. If this is the case, it's plausible that allowing for more UVB exposure indoors would be a net benefit. Previous HN discussion: https://news.ycombinator.com/item?id=18890475 https://news.ycombinator.com/item?id=18890475
- rhinoceraptor 8y agoI don't doubt that sun exposure is a contributing factor to skin cancer, but it just does not make sense that skin cancer rates have shot up over the past 100 years, while at the same time people spend less and less time outside. IMO, there's probably some other causal factor(s), and reducing sunlight exposure is not the solution. Sunlight exposure is important for health, not just for Vitamin D (which others have pointed out, may just be a proxy for some other factor of sun exposure). It's important for regulating circadian rhythm, as well as preventing myopia in childhood.
- copperx 8y agoIf you take a dive on PubMed, you'll see that indeed, sunlight exposure appears to be inversely correlated with all-cause mortality. Why? It is not known, but even when controlling for physical exercise, Vitamin D status, and other factors, the correlation still holds. Some authors suggest other chemicals produced by sunlight, not only Vitamin F, might be involved.
- habosa 8y agoMy grandfather, who was an ophthalmologist with a passion for inventing, has shown me schematics for this kind of glass. His idea was that you could put it in places that are sunny but not warm (like a mountain hotel) to allow for indoor sunbathing. We always make fun of him for this idea as it's one of his strangest. I don't think he ever finished filing the patent.
- amelius 8y ago> So it seems hard to create glass that doesn't block UVB. Ok, so what is the glass in tanning-booths made of? Or the glass of UVB fluorescent lamps?
- duskwuff 8y agoQuartz.
- Florin_Andrei 8y agoThe answer to all such questions is - something related to energy levels of electrons in that material. If there's a resonance somewhere, photons at that energy get absorbed.
- foobar1962 8y agoNikon released a lens in 1984 that offered transmission and correction from UV to IR -- from ultraviolet, through visible light, to infrared (near IR, not heat). http://www.company7.com/nikon/lens/0105f4.5uv.html http://www.company7.com/nikon/lens/0105f4.5uv.html This product was originally announced in 1984 as the Nikon 105mm f/4.5 UV-Micro-Nikkor, and from September 1985 it was marketed as the Nikon UV-Nikkor, then the lens sold then for $2,200.00 USD, then about half the cost of a full sized car.