[pasta]

My question was: "Why does it block UVB?".

Found the answer on Quora: 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.

[kough]

Feynman 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-t...

[Bartweiss]

I'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?

[StrictDabbler]

We 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.

[kragen]

Maybe he should have closed one eye, but the first atomic bomb only explodes once. Your body won't last forever no matter how well you care for it (as Feynman well knew, having just watched his wife Arline die slowly of incurable tuberculosis); seeing the first atomic-bomb test with your own eyes seems eminently worth the risk of blindness, or even sacrificing an eye.

[abdulhaq]

I really can't agree. I would not exchange my eyesight for the whole world, literally. Therefore the qudos of having looked at a novel explosion in no way compensates for any risk to my eyes.

[blotter_paper]

>I would not exchange my eyesight for the whole world, literally.

FYI vacuum exposure can cause blindness, visual impairment, and death.

[Florin_Andrei]

> bright light can never hurt your eyes

Before y'all criticize that statement, keep in mind it's coming from one of the best scientists of the 20th century.

He was talking before lasers. For a purely thermal source to hurt the eyes, it would have to be:

1. insanely hot

2. quite close to the observer

First condition is met by the nuke, but the second one, obviously, is not, unless you're a victim of the explosion.

[ISL]

Scientists, even the best ones, do dumb things all the time.

Source: Am experimental physicist; do dumb things. Sometimes my colleagues do too, even the best ones.

[justin66]

Los Alamos was replete with brilliant people doing dangerously stupid things.

https://en.wikipedia.org/wiki/Demon_core

[Florin_Andrei]

I know. It was not meant as an absolute statement.

[astrodust]

As much as a window blocks UV, I wouldn't trust a laser if a high-powered UV laser was aimed through it at my eye.

[failrate]

I have a scar on my retina near the fovea, and I can only see it if I deliberately focus on it.

[hinkley]

Are we sure he wasn’t wearing sunglasses too?

[Spellchamp]

Yep, 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.

[gist]

> Feynman knew this and claims to be

I don't get this type of thinking. Unless he thought it would be worse to wear the googles what is to be gained by doing something like wearing goggles (in that situation) just in case you were wrong? Why not reduce the chance of harm as much as you can?

[pasta]

Because he was a curious man and wanted to see every detail?

[perl4ever]

I think this also has to be considered in the context of an ongoing cataclysmic war encompassing the world where whole cities were being destroyed and of course they were developing a weapon to destroy them faster. Today, WWII is that long ago thing that lasted for a few years and then it was over. Soon the veterans and the Holocaust survivors will all be dead. To anyone then, a lot of things probably didn't seem as important. A lot of people reacted to the atomic bomb once it was public as the impending end of the world, too. So the scientists who knew about it first probably had their attitudes affected.

[AnIdiotOnTheNet]

There's a fine line between genius and madness.

[brunoqc]

You probably can't see shit with those goggles.

[BurningFrog]

The window didn't block a lot of other high power radiation, and he died from cancer 35 years later, though the connection is not scientifically certain.

[Jaepa]

He was also smoker. He also lived in Los Alamos during its development where the cancer rates where significantly higher

[jsweojtj]

43 years later (Trinity test was in 1945, he died in 1988).

[BurningFrog]

Sorry, my morning coffee must have been weak.

[spuz]

There's a great Applied Science video on the various light absorption properties for various materials here: https://www.youtube.com/watch?v=vwsHRrDYu5o

[harperlee]

So 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.

[JohnJamesRambo]

A good example of what UVA does would be the famous trucker with sun damage to one side of his face-

https://www.huffingtonpost.ca/2012/06/06/bill-mcelligott-sun...

[swebs]

Here's an archive for those getting Oath'd

http://archive.is/aVhiM

[iguy]

Or the source: https://www.nejm.org/doi/full/10.1056/NEJMicm1104059

[JCharante]

Well this has made me reconsider my lack of use of sun screen. Thanks for sharing.

[JohnJamesRambo]

I'm stuck between a rock and a hard place because this article makes a lot of sense.

https://www.outsideonline.com/2380751/sunscreen-sun-exposure...

I think I'm just going to use daily sunscreen on my face only.

[astazangasta]

Melanoma is definitely due to DNA damage; somatic mutation is the principal cause of all cancer. In this case the cause is either direct damage or damage by free radical byproducts created by UV. UV causes a kind of mutation in DNA called a pyrimidine dimer, where two adjacent bases mutate at once. By far the most common mutation in melanoma (reponsible for 50% of cases) is a CC to TT mutation at position 600 of the gene BRAF.

[logfromblammo]

The 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]

Well, 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.

[moftz]

UVB causes melanoma, that is also a form of cancer. So typical glass would prevent sunburn and melanomas from forming but not the deep genetic and tissue damage that UVA causes. It is not a bad idea to apply SPF moisturizer before going out if you plan to spend anytime with the sun shining on you.

[dzhiurgis]

UVA causes DNA damage (and potentially cancer) indirectly via oxidation.

From what I read UVB melanoma is an "easy" type of cancer.

[taneq]

> So in case anyone just panicked thinking “Wait, so do my car and office windows block cancer producing UV or not??”

I just figured automotive glass doesn't block UV (or at least all of it) since window tinting places always advertise UV blocking as a feature of their films. Cynically I know it could be just empty marketing, but it didn't seem like it.

[Nomentatus]

Of course, ordinary light, while still less energetic, penetrates still more deeply into skin, and it, too causes DNA damage. In situ DNA is damaged by light absorbed by less transparent molecules it is near.

[garmaine]

Why are you assuming there isn’t DNA damage when sunburned?

[hopler]

Not that there's no damage, but that sunburned skin is top layer skin that is constantly shedding so won't accumulate damage for decades

[garmaine]

Only the most burnt skin is shed. The UV light penetrates further layers.

[Etheryte]

Quartz 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]

Sapphire's also transparent down to far ultraviolet (150nm). Not sure about ALON.

[masklinn]

Replying to self (because the edit window has gone): ALON apparently goes down to 200nm, so it's transparent to UVB (280-315)

[Florin_Andrei]

Sapphire 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.

[foobar1962]

Nikon 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

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.

[rjf72]

Mildly 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

[hopler]

Other comments say glass does not block UVA

[habosa]

My 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.

[tomcam]

I mean this as politely as possible: why would you make fun of someone developing in an unusual idea?

[habosa]

I don't think I need to explain teasing a family member in terms of the HN worldview.

[copperx]

And as a follow-up question, what are you doing in HN?

[devy]

> 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

[tlals]

There 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

[rhinoceraptor]

I 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]

If 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.

[copperx]

(correction to above, I meant Vitamin D, not F, of course).

[com2kid]

> Physics aside, why would you want to do that in the first place?

I worked on a product that had a UV sensor. It needed to be protected.

Sourcing glass that didn't block UVB, that could be used in a mass market product, at cost, integrated into a manufacturing line, was a bit of a challenge. The mechanical engineering team eventually got a hold of some. For awhile, there were weekly status updates of "got another manufacturing sample, spec sheet wasn't quite honest, it blocks some UVB."

[C1sc0cat]

Depends for some skin conditions its better to have timed exposure via UVB therapy - I have had this in the past.

[Florin_Andrei]

The 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.

[amelius]

> 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]

Quartz.

[lightedman]

Soda-lime glass transmits pretty much all UV ranges and is readily manufactured (it is used often in germicidal lamps.)

[vanderZwan]

You 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.

[Waterluvian]

I think you're inverting what parent is saying. Glass by nature seems to block UVB.

[vanderZwan]

Ah, right. I somehow thought GP suggested near the end that it seems to be hard to fabricate glass that blocks UVA, and answered the question of how to deal with that.

[georgyo]

How does coating it prevent the glass itself absorbing UVB?

[vanderZwan]

As Waterluvian pointed out, I misread GP and explained how we could make glass block UVA as well.

[losvedir]

Ah, yes the classic "government intervention to attack a misunderstood problem with a solution that won't work".

[vanderZwan]

Ah 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]

Well 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]

Did you read the other comments? I misread GP and the coating I talked about is for UVA radiation.