Do polarized sunglasses protect against snow blindness?

One of the classic applications of polarized sunglasses is to skiing. Light from the sun is unpolarized, but when it is reflected from a surface at a glancing angle, it becomes highly polarized. When you're on a snow field, a lot of the bright light getting into your eyes is light reflected from the snow, and when the sun is low in the sky, this glare is coming from glancing reflection, so it's highly polarized. If you wear polarized sunglasses, they will help to cut out this glare disproportionately, making it easier to see other stuff without having your view interfered with by the intense glare.

This is all about comfort and ease of seeing, but doesn't necessarily tell you anything about snow blindness. Snow blindness is mainly caused by UV, which you can't perceive and which doesn't cause immediate pain or discomfort. In addition to snow blindness, UVB (and possibly UVA, although the evidence is not as strong) can cause long-terms problems with vision.

So then the question is whether polarizing lenses are or are not effective against UV. We have a separate question about that, but basically the answer is that they're probably pretty darn effective, but probably not as effective as you'd ideally like.

posted almost 10 years ago

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Ben Crowell‭

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There are actual standards for this. If you are going somewhere where snow blindness is a real possibility, you should have sunglasses that meet the standard. The most common standard used in outdoor sunglasses is the Category standard based on the european CE standards. There are 5 categories 0-4

This page has a good overview:

An Explication of Sunglasses Lens Categories.

Basically, general purpose outdoor sunglasses should be in Category 3, which is appropriate for skiing in the winter when the sun is generally at a low angle. If you are climbing a glacier in the summer, you want category 4 level glasses.

Polarized lens can certainly help, but ultimately it's the reduction in UV light levels that prevents snow blindness.

posted almost 10 years ago

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Fred the Magic Wonder Dog‭

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Any sunglasses or will help protect against snow blindness. UV protection is highly recommended.

posted almost 13 years ago

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xpda‭

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Regular polarized sunglasses are usually meant for drivers of cars, as these glasses, in addition to darkening the sky, also suppress glare/reflections.

If you travel in snow, light will come from all different angles and directions and will therefore be polarized in all kinds of directions, so a mere polarizer will not filter a sufficient amount of light. I learned this the hard way...

So in addition to a polarizer, any goggles you use in the outdoors should have something that darkens independent of orientation. How much depends on where you want to go. Just in the mountains where there is some snow, or onto glaciers and ice fields where you'll see nothing but snow for days. I don't know the numbers off the top of my head, but I know that the goggles I use for trekking are so dark that I'm not allowed to wear them while driving (some 99% reduction, I believe). This is something people in an outdoors store should be able to explain to you.

Another very important thing to watch out for is stray light. What I also learned the hard way is that clip-on sunshades for your regular glasses let too much light in from the sides. You want to make sure that once you wear your goggles, any light that reaches your eyes must travel through the glasses. Again, on a glacier or in snow, light comes from all directions. Serious expedition-style goggles therefore look a bit like old pilot's goggles, with leather at the sides preventing any stray light from sneaking in.

posted almost 13 years ago

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Lagerbaer‭

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I wear polarized lenses in snow, even at night; and when I come back indoors I can see everything just fine. If I spend significant time outdoors in blanketed snow, even at night, without my polarized glasses on, when I come back indoors I am basically blind or searching for focus until a number of minutes have passed.

posted over 9 years ago

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deckked‭

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Contrary to what some may feel is a limited use for polarization the sole purpose of this filtering is to minimize glare directly and indirectly caused by but not limited to bright sunlight. By doing so your visual acuity is increased in any bright light environment. Keep in mind light itself travels so it will bounce off any reflective surface. The more reflective your environment is the more intensive the glare will be.

The most effective way to protect your eyes from harsh reflection is polarization. There are several levels of quality to this filter so dont be to surprised if cheap (low end) protection doesn't do the job. In addition to a higher quality filter, choose a color that best suits the environment you are in most often, the amount of allowable light transmission is critical to expected performance. The frame you select is just as important as color, wrapped coverage for the sportsman will help maximize your vision by blocking the amount of light coming in from the sides as where the casual activity sunglass wearer will be just fine with a fashion style frame.

posted almost 10 years ago

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user5585‭

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Regular sunglasses should give you protection from snow blindness, so long as they protect against UV radiation. How well they protect you is dependent on how well the lenses cover your eyes, and how well the lenses or coatings filter or deflect UV radiation.

posted almost 13 years ago

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mendota‭

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