When most people need a pair of sunglasses, it is usually because the sun is beating down on them and they want to block out the glare. Many go to the first place they can find whether at a dollar store or some mass merchandiser, not even thinking about whether they are polarized, what kind of UV amounts they are blocking out, how much protection from glare they have. It isn’t until later that it is realized that you get what you pay for.
Polarization is a film that covers the surface of the lens, filtering out all light except ones that are aligned with this film. It will let in light that allows you to see objects and colors, but not UV light or other rays that not only cause glare, but can actually damage the eyes in the long run. Now a good pair of sunglasses should have at least four layers to it. An anti-reflective coating on the inside, the lens, a polarizing film and the scratch resistant coating. Some will have mirror finishes on them as well, and this optional coating can be just about anything from holograms to rainbow reflective mirrors.
Now to completely discuss about the suns rays, light spectrum, how we see color and the definition of what visible light is would be quite extensive. There are many scientific studies available online to explain how bad glare is for your eyes and UV rays. In short, intensity of light is measured in lumens. When you are inside, artificial light is around 4-600 lumens, but on a sunny day, outside, a reflective surface can be more that 6000 lumens. Anything past 3500 and your pupils start to contract and if that doesn’t work you start to squint. If you eyes continue to be exposed they start blocking out all light, causing temporary or even permanent blindness.
Just take your time when picking out glasses, and do some researching first. One big new thing about lenses these days is you have an assortment to choose from. Along with the traditional gray that most people have grown up with, there are also copper tinted lenses that provide better depth perception, and yellow color that effectively brightens night vision, but without glare from oncoming headlights. Sometimes you will find that these special lenses may be a little expensive, but if they are quality products they will provide years of use, or at least until you break or lose them.
You may also find clip on style polarized lenses for prescription glasses. Be wary of these because if they are not made right they could break easily. You will want ones that have some kind of covering over the clips, and that are light enough that they don’t put too much pressure on the bridge of your nose.
James Thompson writes for the Designer Sunglasses website, specializing in Dolce And Gabbana sunglasses