What
exactly are UV rays?
Ultraviolet (UV) rays are located just past the violet portion of the
visible light spectrum; sunlight is the main source. UV light is broken into
three different types: UVA, UVB and UVC. UVA has longer wavelengths and
passes through glass easily; experts disagree about whether or not UVA
damages the eyes. UVB rays are the most dangerous, making sunglasses and
sunscreen a must; they don't go through glass. UVC rays do not reach the
Earth because its atmosphere blocks them.
Most people think that they're only at risk when they're outside on a sunny
day, but UV light can go right through clouds, so it doesn't matter if the
sky is overcast. The sun's rays are strongest between 10 am and 2 pm.
Glare and reflections can give you trouble, so have your sunglasses ready if
you'll be around snow, water or sand, or if you'll be driving (windshields
are a big glare source).
The following put you at additional risk: sunlamps, tanning beds and
parlors, photosensitizing drugs, and living at high altitudes or near the
equator.
Infrared rays are located just past the red portion of the
visible light spectrum. While some experts believe that infrared light can
be harmful in certain situations (such as being near large bodies of water
or at high altitudes), most feel that the sun's infrared rays do not pose a
danger to the eyes.
Color is a personal choice and doesn't affect how well the lenses protect
your eyes from UV light. Gray and brown are popular because they distort
colors the least. Athletes may choose other tints for their color-enhancing
properties; for example, yellow lenses are popular with skiers and target
shooters because they work well in low light, reduce haze and increase
contrast for a sharper image.
Gray tints are great all-purpose tints that reduce the
overall amount of brightness with the least amount of color distortion. Gray
lenses offer good protection against glare, making them a good choice for
driving and general use.
Amber and brownish tints are also good general purpose tints. They have the
added benefit of reducing glare and have molecules that absorb higher
frequency colors, such as blue, in addition to UV rays. There has been
research that suggests that near-UV light frequencies such as blue and
violet can contribute to the formation of cataracts over time.
Green tints on lenses filter some blue light and reduce glare. Because green
tints offer the highest contrast and greatest visual acuity of any tint,
they are very popular.
Purple and rose tints offer the best contrast of objects against a green or
blue background. They make a good choice for hunting or water skiing.
Polarized filters are most commonly made of a chemical film
applied to a transparent plastic or glass surface. The chemical compound
used will typically be composed of molecules that naturally align in
parallel relation to one another. When applied uniformly to the lens, the
molecules create a microscopic filter that absorbs any light matching their
alignment.
Most of the glare that causes you to wear sunglasses comes from horizontal
surfaces, such as water or a highway. When light strikes a surface, the
reflected waves are polarized to match the angle of that surface. So, a
highly reflective horizontal surface, such as a lake, will produce a lot of
horizontally polarized light. Therefore, the polarized lenses in sunglasses
are fixed at an angle that only allows vertically polarized light to enter.
You can see this for yourself by putting on a pair of polarized sunglasses
and looking at a horizontal reflective surface, like the hood of a car.
Slowly tilt your head to the right or left. You will notice that the glare
off the surface brightens as you adjust the angle of your view.
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.
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