Eye safety questions

[Muslim]

I was reading a book about Richard Feynman, one of the scientists that build the atomic bomb, and at some point he describe the first explosion.
Here is the quote:

For people who were far away like we were- others were closer, sex miles away- they gave out dark glasses that you could watch in with. Dark glasses!! Twenty miles away of the damn thing, you get dark glasses- you couldn't see a damn thing thorough dark glasses. So then I figured the only thing that could really hurt your eyes-bright light can never hurt your eyes-it's ultraviolet light that does. So I got behind a truck windshield, so the ultraviolet can't go thorough glass, so that would be safe, and so I clouds see the damn thing. OK. Times comes, and this tremendous flash out there, so bright I quickly see this purple splotch on the floor of the truck. I said "that ain't it, That's an afterimage." So I turn back up and I see this white light changing into yellow and then into orange. The clouds form and them they disappear again, the compression and the expansion forms and makes clouds disappear. Then finally, a big ball of orange, the center that was so bright, became a ball of orange that stated to rise and billow a little bit and get a little black around the edges and then you see it's a big ball of smoke with flashes on the inside of the fire going out, the heat. I saw all that and all this that I just described in just a moment; took about one minute. It was a series from bright to dark and I had seen it. I am about the only guy that actually looked at the damn thing, the first trinity test.

The question's are:
Is it true that only ultraviolet light can damage your eyes?
Is it true that you can protect yourself by using just glass?

Another thing:
I often see some warnings in some telescopes that say that you shouldn't use it on the sun or near it, because it will irreversible damage your eyes.
I think that looking to the sun through a telescope should be safer than looking at it with naked eye. Basically what a telescope do is to expand some part of the image into a larger image. The resulting image should have less energy per area in it than the original image, and no ultraviolet in it too, so it should be safer.
But I thrust those warnings, so it must have something wrong with my logic.

 

[Zombified]

Any light can damage the eye if there's enough of it, by heating effects. For example, any laser of enough power, including an infrared laser, can damage your eye. (Infrared is lower frequency, or energy-per-photon, than visible light, while ultraviolt is higher.)

Ultraviolet does more damage because its higher energy can damage some molecules directly, not just by heating.

Looking at or near the sun with a telescope or binoculars is very dangerous to your vision. Don't do it. Normally, the light gathering power of your eye is the width of your pupil. However, with the telescope, the light gathering power is the size of the object lens. Think about how much bigger the telescope lens is than the lens of your eye, that's how much more light and heat is going into your eyeball.

It's just like using a magnifying glass to ignite a piece of paper in the sun. You really don't want to do that to your eye.

 

[geni]

Another thing:
I often see some warnings in some telescopes that say that you shouldn't use it on the sun or near it, because it will irreversible damage your eyes.
I think that looking to the sun through a telescope should be safer than looking at it with naked eye. Basically what a telescope do is to expand some part of the image into a larger image. The resulting image should have less energy per area in it than the original image, and no ultraviolet in it too, so it should be safer.
But I thrust those warnings, so it must have something wrong with my logic.

Definetly not. A telascope works by collecting light over a larger area and focusing it on a small area. Looking through a telescope at the sun would have a simular effect on your eye as focuing a magnifying glass on an ant only more so. So DON'T DO IT.

 

[Virgil]

The question's are:
Is it true that only ultraviolet light can damage your eyes?
Is it true that you can protect yourself by using just glass?

no, both UV and IR will damage your eyes. I'm not sure about powerful normal light.


If it is thick enough and the right kind of glass. ie quartz is transparent to some UV light. it will depend upon wavelength of the UV lamp.

looking at the sun long enough will cause you to go blind forever.
don't know if it is UV or brightness.

disclaimer: This is not medical advice.
Virgil

 

[richardm]

That's actually an interesting question.

One other problem with damage from UV is that you can't see it. Combined with the fact that you have no feeling on your retina, you can do a lot of damage and not realise until you notice the black splodges in your vision.

 

[Zombified]

Visible light alone will damage your eye if there's enough of it, or if it's concentrated enough. Example: visible light laser (assuming it has enough power).

Of course, its easy to realize when you're looking at a bright visible light source and you generally have an immediate reaction of closing your eyes or looking away, so visible lasers are less dangerous than infrared lasers for that reason even at the same power level: you could stare at an IR laser and not realize it even though considerable damage is being done.

 

[Iconoclast]

I was reading a book about Richard Feynman, one of the scientists that build the atomic bomb, and at some point he describe the first explosion.

The question's are:
Is it true that only ultraviolet light can damage your eyes?
Is it true that you can protect yourself by using just glass?

That quote appears in many of Feynamn's books, his publisher just kept churning out different titles that were collections of his essays, and as a result the same essays appear in several different books. I think Feynman meant that a bright IR flash wouldn't damage your eyes, I have no idea if this is true. I think he was actually looking through the polarised part of the truck windscreen to filter out the UV though he doesn't explictily say this. However, in Richard Rhodes' epic account of "The Making of the Atomic Bomb", he credits a DIFFERENT scientist (can't remember who) with being the only person to see the Trinity bomb explode by looking through the windscreen of a truck. Feynman was never one to lie though.