That’s a good explanation for why the sun is less intense at dusk and dawn.
Additionally if the light is coming in from the side, you may not even notice if it causes damage. The lens focuses incoming light on the fovea which is basically the center of vision. You may not notice damage to the periphery of your vision until it becomes severe.
First of all, electromagnetic radiation is a whole range of stuff. Starting at the low end (frequency-wise) you’ve got long waves (useful for submarines to communicate through polar ice but not much else), radio waves, microwaves (which are really just higher frequency radio waves), infrared light, visible light, ultraviolet light, x-rays, gamma rays, and cosmic rays.
The lower frequency stuff is less harmful than the higher frequency stuff. This is because part way through the ultraviolet part of the spectrum, electromagnetic radiation becomes “ionizing” meaning that it can strip the electrons off of atoms and create ions. Ionizing radiation is known to be very harmful to all kinds of stuff. This is why ultraviolet light causes things to fade if it is left out in the sun, and it’s why sunlight causes skin cancer and why x-rays cause cancer. So some of the ultraviolet stuff and everything else higher (x-rays, gamma rays, cosmic rays) is ionizing and is very dangerous. This is the stuff that most folks are talking about when they use the term “radiation”.
Lower frequency stuff isn’t so dangerous. You can shine a flashlight on your skin and it won’t hurt you (you wouldn’t want to do the same thing with a flashlight that put out the same relative level of x-rays). Cell phones use microwaves, and despite millions of panicked people on the internet saying otherwise, these are too low in frequency to be harmful in the same way that x-rays and gamma rays are.
That doesn’t mean that the lower frequency stuff is completely harmless though. We are used to visible light being harmless because most of the time when we encounter it, the amount of it striking us is harmless. A flashlight, for example, is too low in power level to be harmful. Get the power level high enough though and you can cause all kinds of damage. This is how microwave ovens cook things. Cell phone levels, like a flashlight, are completely harmless. Microwave ovens use the exact same type of radiation (microwaves) and will cook food. Visible light can cook things, too. Just ask anyone who has ever fried an ant with a magnifying glass and sunlight. Lasers can certainly cause quite a bit of heat.
Your eye’s retina is very delicate, and can be much more easily damaged by both ionizing and non-ionizing radiation than other parts of your body. Sunlight will burn your retinas to the point of destruction but will only make the skin on your arms feel warm. Your skin is just tougher, and your retinas are just that easily damaged. So it’s not surprising that the very bright light from a welder can damage your retinas.
Welders also put out UV light. If you are looking away from the welder you can prevent the visible light from damaging your retina, but the UV light might still strike your corneas. Remember, UV light is ionizing. It is more dangerous. In this case, repeated exposure to your corneas will likely cause cataracts to develop. For similar reasons, a lot of sunglasses these days have lenses that wrap around to the side to prevent the sun’s UV light from striking your corneas from the side.
So basically, welders can hurt your eyes in two ways. First, the intense power levels of visible light can burn your delicate retinas in the same way that a microwave oven cooks food, just by having a large amount of electromagnetic radiation there. Second, the UV light can cause cataracts, even if it doesn’t strike your retina. Welding goggles prevent both problems.
looking at the sun directly should not cause thermal damage to the retina, the UV might hurt your corneas but all damage should be temporary (along with the annoying-ass afterimage)
I once got a minor, but very aggravating, case of cornea burn (which, as Kevbo said, feels like having grains of sand in your eyes, but nothing you do gets rid of them) just from indirect exposure to a welding arc for about 90 seconds while my brother was welding. I knew better than to look at the arc itself, having been warned “Don’t look at the bright purple!” ever since I was a toddler, but I didn’t realize that the diffuse purple reflection of the arc off the shiny concrete wall was going to be enough to hurt my eyes if I got close enough. Ouch…
I work in a welding shop. I’ve been flashed a lot by the welders. If it’s only a couple of times a day, I’m not bothered much. But sometimes I get it pretty bad, and at the end of the day my eyes feel so dry that I could use a gallon of Visine and it wouldn’t help that much. Once in a while I’m fast enough to get a pair of brazing glasses to cut down the glare enough to help, but so that I can still work and see what I’m doing. It’s a hazard that comes with the territory, really. Our company has recently started putting more emphasis on making sure welders pull their curtains to protect other people on the floor from that, thank goodness.
There have been reports of permanent damage in the cases of “sungazers”.
There’s apparently some evidence that it can still damage the retina. We had a discussion about this subject in this thread a year or so ago; especially interesting are lazybratsche’s posts, such as the one here, which links to and summarizes a thorough discussion on the subject. (It should be obvious that SunGazer’s posts are just plain nuts, I would hope.)
Back when the Transit Of Venus was happening I was trying to take some pictures of it and made the bone headed mistake of looking into my camera before I put the filter on it and without my eclipse glasses on.
A few days later my eyes were still bugging me. Trying to see how long it was going to bother me for I ran across a lot of people that accidentally looked at welding arcs and they did some bizarre thing to their eyes that was supposed to help (but probably doesn’t). Now I’m going to have to go look it up.
ETA potatoes. That’s what it was. Half the people said to put potatoes on your eyes, the others said to go to a doctor and get some kind of eye drops.
I’ve heard of the potato thing too. I’m guessing that the coolness of the potato might provide some relief but it can’t last very long.
How long were you looking at the sun that it ended up hurting your eyes? Did you immediately realize the mistake and stop to put the filter in, but your eyes had been damaged pretty much instantly? Or were you looking at the sun for a while before you realized the filter wasn’t in?
One factor is distance. Intensity is inversely proportional to the square of the distance from the source. The guy holding the torch has his face about 12 inches from what he’s welding. If you’re six feet away, then the intensity of the radiation reaching you is 1/36 of what reaches him.
It also depends on the type of welding. In stick welding, there’s more smoke that tends to block a lot of light from escaping the scene. In TIG/GTAW welding, there’s very little smoke, so most of the generated light escapes.
Personal account:
I once had a project where I had to do some tack-welding (this is where you don’t use any filler metal and just hit your parts with a very brief blast of high current, like a fraction of a second, melting a tiny amount of the parent metal to hold the parts together so you can weld it up later without having to clamp anything). Not having an auto-darkening welding helmet, I just closed my eyes and blasted the parts. Without thinking too much about it, I did a bunch of tack-welds like this. 180 of them in a row. All told, I exposed my face to maybe a minute of radiation. I developed a severe, blistering sunburn on my face. A couple of days later I went and bought an auto-dark helmet so I would never again be tempted to tack-weld with a bare face. :smack:
Near the end of this page,, there’s a table showing the optical properties of some common welding shields. “Shade 10” is a level that’s commonly recommended for general stick/TIG/wire welding. As you can see from the numbers, it blocks the vast majority of incident light. If you’ve never looked through one of these, it’s pretty dark under normal lighting conditions; you’d have some difficulty navigating a cubicle-laden office area. But it’s perfect for welding - the arc and its immediate surroundings are bright and easy to see, but not overwhelming.
Here’s the cutting edge of technology for welding visualization: HDR welding imaging. Cameras capture the welding scene and compress the huge range of illumination intensities down to something that can be displayed on a monitor. Now you can see not just the arc, but also the surrounding scene, all very clearly.
If I ask incredulously for a cite, will I hear a whoosh?
Otherwise, cite?
My welding improved a lot after I learned that I didn’t need to keep it at arms length, which is closer to 3 feet for me. For some reason the arc intimidated me a lot, and I was trying to keep my face as far back as possible.
Looks like there’s at least a grain of truth to it.
Fumes/smoke can be an issue if you get ridiculously close, but good ventilation can minimize this.
Getting close enough can be difficult as we age and our eyes lose their ability to focus at close range. Welding shops often sell “cheater” lenses like this one, basically a pair of magnifying glasses that clip inside your welding helmet.