So your irises open up and you get a much higher relative dose of UV.īecause it will cause you damage to your eyes, and eventually blind you. But the clouds aren't blocking the UV much at all, so you're still getting the same UV penetration through the atmosphere. Your irises will open up to let in more visible light, since it's cloudy and there's a little less of it. This is also why cloudy days can be very dangerous for your eyes. But the Sun is bright enough, especially in the UV spectrum, that your irises can't close enough to protect you. That's why we have irises: to control how much gets into our eyes so we don't overwhelm them. Remember, their whole purpose is to absorb light, and they need to be sensitive enough to pick up the tiny bits of light at night. But when you look at the Sun, you get a direct dose of UV that isn't being filtered by anything else - the ground isn't absorbing it, your skin isn't absorbing it, it's going straight to your retina (* actually a lot of UV gets filtered by the atmosphere, but there's still a lot left to hurt your eyes).Īnd your retinas are very sensitive. ![]() There's still some, but not enough to cause problems. Luckily, most things absorb UV pretty readily, so looking around you don't get a whole lot of UV coming into your eyes. Sure, you don't want the UV light, you can't see it, but you can't get the visible spectrum into your eyes without also letting in some UV. More than any other part of your body, they are the most vulnerable to UV damage, because you are inviting light into them. Your eyes, you may notice, are transparent, for obvious reasons. If that chemical bond happens to be in your DNA, and it falls apart, you get cancer. Without diving into a different ELI5, the short version is that UV light has enough energy to knock electrons off your atoms, which can really jack up the chemical bonds. ![]() UV is dangerous because it's what's called ionizing radiation. Your skin does a lot of work blocking out dangerous UV light.
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