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Is it simply the amount of visible light entering the eye? I'm simply confused as to why experts say that sunglasses do not provide adequate protection when they are advertised as blocking 100% of the sun's harmful rays.

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    $\begingroup$ Sunglasses primarily restrict specific wavelengths of the electromagnetic spectrum (ultra violet, as mentioned), but neglect to fully restrict visible light. If (every day) sunglasses were designed to restrict enough visible light so that we could safely stare at the sun, then we wouldn't be able to see anything else! $\endgroup$ – user22020 Aug 3 '17 at 21:53
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The damage to your eye does not only come from UV exposure, but also from infrared (IR) radiation. Your eye contains a lens that focuses the incoming rays to a narrow point. This point would get very hot if you looked directly into the sun. This is comparable to focussing the sun on a piece of paper with a magnifying glass, it would start to burn. Also, the rods and cones in your retina are only tolerant to a certain exposure of visible light.

Source: https://eclipse.gsfc.nasa.gov/SEhelp/safety2.html

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  • $\begingroup$ The page you provided as a source is quite extensive. Would it be possible for you to quote the portion pertaining to infrared? Thanks. $\endgroup$ – user22020 Aug 3 '17 at 22:30
  • $\begingroup$ Thanks so much for the source you provided, I had a really hard time finding the information I wanted that gave specifics as to the different dangers of looking at the sun besides "Don't do it." It seems like the main problem is the visible light which is what I suspected, although even in the source it is unclear whether hen they are talking about IR whether it is truly the IR radiation or the near IR radiation (or essentially more visible light) that contributes to the issue. Regardless, thanks for your help! $\endgroup$ – johnny Aug 4 '17 at 15:08
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Visible light too is dangerous to have concentrated into your retina.

When you shine a flashlight at yourself, where does all that visible light go as it seemingly disappears into your body?

Heat!

It makes your molecules more ever so slightly more.

Also, a lot (but not all) of the uv light is absorbed by your cornea.

Visible light will enter your retina, and focused to a point that is REALLY DANGEROUS. The heat from the light hitting your retina will immediately denature all the proteins inside your retina cells, killing them.

This will happen no matter how much IR or UV you block.

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