Do polarized sunglasses protect against UV?

The basic idea of polarizing glasses is not to block all light, it's to block light that undergoes a glancing reflection, such as sunlight coming to your eye off of water or snow from near the horizon. The initially unpolarized light becomes highly polarized by this type of reflection, so by eliminating it, you make it easier to see and be comfortable without the blinding glare, while still allowing a lot of the unpolarized light that you want to see to get to your eye.

A polarizing filter can have varying degrees of effectiveness at various wavelengths. An ideal polarizing filter would block 100% of the light with a particular polarization, regardless of wavelength, and would block 0% of the light with the other polarization, regardless of wavelength. In reality, polarizing filters have efficiencies that depend on wavelength. This article has a graph for polaroid film, which is just one type of polarizing filter. It shows that in the UV band, the filter is almost perfect at blocking the polarization it's supposed to block, and that furthermore it blocks about 70-85% of UVB polarized the other way, depending on the exact wavelength. So if you have sunglasses that have this specific type of filter, then it's going to do a very, very good job of blocking the highly polarized UVB that comes to your eye from glancing reflection off of water or snow, and furthermore it will be at least somewhat effective in protecting you from the other polarization as well. But this filter all by itself will not do a super-great job of protecting you from unpolarized light, such as light that comes directly from the sun. For these reasons, if you're going to be on glaciers for many hours a day, in bright sun, it would be preferable to have not just sunglasses that have a polarizing film, but also a highly effective special-purpose filter that blocks UV in general.

Complicating all of this, we have several factors:

• Depending on the style of sunglasses and where you have them positioned on your face, as much as half of the light can get in the sides.

• Sunglasses are often labeled as polarizing when they actually aren't. (But this is easily tested once you have the glasses in your hands.)

• Standards bodies have apparently decided that "100% UV protection" only really has to mean 95% UV protection from UVB. (Of course exactly 100% is mathematically impossible.)

• You probably have no way of knowing what specific polarizing material is being used, and therefore you don't know how that filter acts on polarized UV.

So any sunglasses are better than nothing, polarizing sunglasses are quite good, and sunglasses with both a polarizing filter and a UV filter are better. However, you may have a very difficult time finding out whether the glasses you buy really are what they claim to be.

posted over 9 years ago

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Ben Crowell‭

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Polarized sunglasses, as with other type of sunglasses may not block enough UV to be considered safe.

From WikiPedia:

for adequate protection, experts recommend sunglasses that reflect or filter out 99-100% of UVA and UVB light, with wavelengths up to 400 nm. Sunglasses which meet this requirement are often labeled as "UV400.

In other words, you have to check the manufacturer's information on what degree of UV protection the sunglasses afford, polarized or not.

posted over 10 years ago

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Paul Lydon‭

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The answers all correct, but the main questions is, Does unique Polarized glasses protect from UV rays? Yes...up to some extent (some percentage).That is, when polarized glasses block the horizontally polarized light from SUN, It also blocks the UV rays which are horizontally polarized. So one can protect from UV rays by using Polarized glasses up to some extent. Use polarized glasses where there is a glare & Bright SUN, if Polarized+UV glasses are not available. But do not use the UV only glasses where there is a glare. Use Polarized+UV glasses at any situation, i mean UV bright SUN only or Glare only or both. The purposes of the both the glasses are different. one for UV and other for glare.

posted about 9 years ago

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M.V.Ramesh‭

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Polarization and UV protection on sunglasses are two different things. While UV refers to light of a wavelength of approximately 10nm to 400nm, light of any wavelength can be polarized. Sunglasses with a polarization filter block light, that is horizontally polarized (e.g. light reflected on water). This has no specific effect on UV-light. So polarized sunglasses do not generally protect against UV, they also need a filter dedicated to blocking UV-light.

As I suspect the question arises because it is not clear what the use of a polarization filter in sunglasses is, some background information on this topic:
Light emitted by the sun oscillates in all directions perpendicular to the direction it travels. When reflected on a surface such as a lake, it becomes polarized parallel to the surface of the lake. This means, the light only oscillates along the axis parallel to the surface in the plane perpendicular to the direction it travels. Polarized sunglasses block horizontally polarized light, in order to protect your eyes from these strong reflections. Polarization in the sky occurs when light scatters the molecules in the atmosphere. A good explanation can be found on the Polarized Light site.

posted over 10 years ago

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imsodin‭

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Polarization alone makes no difference to UV protection where it most matters: the interior of your eyes, especially your retinas and vitreous humor.

Although the polarized glass blocks a proportion of incoming light, the proportion of that light which is UV is (roughly speaking) unchanged. The reason that the ratio of UV to visible light is important is that the eye adapts very well to the intensity of daylight, opening the iris to admit more light when you wear the sunglasses.

You need to ensure that your sunglasses provide UV protection whether or not they are polarized - look for conformance to ISO 12312 or equivalent, and (where applicable) a CE mark.

posted almost 8 years ago

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Toby Speight‭

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