I wanted to suggest that you include comments about polarizing sunglasses as part of the "Sun Essentials" page on your Web site. This type of sunglasses is the only thing that can protect eyes from harmful effects of the sun--not to mention the skin around the eyes.
Nikki, via email
You're right--without question, sunglasses are a major part of protecting your eyes when you're outdoors, even on cloudy days. However, polarized sunglasses are not really about sun protection, a fact many consumers are probably unaware of. (Most of the people in my office were surprised when we discussed your letter.) The primary purpose and benefit of polarized lenses is glare reduction. Glare is concentrated light reflected in a specific direction off a surface, and is often bright enough to temporarily blind you. Classic examples of glare are sunlight reflecting off of horizontal surfaces such as snow or a wet road, with snow glare being particularly bothersome, not to mention dangerous. Polarized lenses remove glare because they have a layer of vertical stripes imprinted on sheets of polyvinyl alcohol (PVA). These stripes eliminate common types of horizontal glare by allowing only vertical light to pass through the lens, while the light coming from other angles is absorbed. The amount of polarization a lens achieves is proportional to the density of its PVA film. Lighter films offer less polarization and thus less glare reduction.
The polarizing material used to make the lenses in safety eyewear is created by sandwiching PVA between two layers of polycarbonate. Polycarbonate is inherently UV protective, so polarizing safety glasses perform three functions: (1) they protect eyes from actual physical impact (as required by ANSI Z87.1 2003, the high-impact standard), (2) they protect eyes from glare coming from horizontal surfaces, and (3) they protect eyes from harmful UV rays. Safety glasses, however, aren't the same thing as sunglasses. For sunglasses (polarizing or not) to protect eyes from UV light, a UV-inhibiting coating must be applied to the lenses. Fortunately, most major manufacturers of polarizing sunglasses include this coating as part of the process, which is why many people, including eye-care professionals, believe that polarizing lenses also protect your eyes from UV light. That is not the case. So, if the polarizing sunglasses you're considering do not have a label indicating 100% UV protection, keep shopping! Interestingly, darker sunglasses do not necessarily offer better protection. The UV protection a pair of sunglasses offers depends on a clear chemical coating that is applied to the lens, so the darkness of the lens is not as much of a deciding factor as many people think (although if your eyes are sensitive to bright or overcast light, darker lenses are preferred).
One more point, according to www.howstuff works.com, "A lot of sunglasses advertised as polarizing actually are not. There's a simple test you can perform before you buy them to make sure. Find a reflective surface, and hold the glasses so that you are viewing the surface through one of the lenses. Now slowly rotate the glasses to a 90-degree angle, and see if the reflective glare diminishes or increases. If the sunglasses are polarized, you will see a significant diminishing of the glare."
Source: Paula Begoun