TN Sunglasses

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					                       Tennessee
    Consumer Decision Judging Guide
                              Sunglasses
      If it’s a bright, clear day outside, you may instinctively reach for your
sunglasses, when you head outside. Choosing sunglasses for eye protection allows
a wide range of choice. Knowing what features are available will help in finding
the best pair of sunglasses for the conditions in which they will be worn.

       There are four things that a good pair of sunglasses should do for you:
1. Sunglasses provide protection from ultraviolet rays in sunlight. Ultraviolet
(UV) light damages the cornea and the retina.
2. Sunglasses provide protection from intense light. When the eye receives too
much light, it naturally closes the iris. Once it has closed the iris as far as it can,
the next step is squinting. The result of too much light is damage to the retina.
A good set of sunglasses can block light from entering the eyes thereby avoiding
damage.
3. Sunglasses provide protection from glare. Water and some surfaces can
reflect a great deal of light. These reflected spots can hide objects and be
distracting, especially to drivers.
4. Sunglasses eliminate specific frequencies of light. Certain frequencies of
light can blur vision and others can enhance contrast. Choosing the right color
sunglasses enables them to work better in certain situations.

Light
       Much of the concern over eye health involves the shorter wavelengths,
called ultraviolet (UV) light. UV light is divided into two categories- (1) shorter
wavelengths are called UVB, longer wavelengths are called UVA. Shorter waves
have been found to cause more eye damage than longer waves. The main
protection offered by sunglasses is filtering out these UV rays. The dark color of
the lenses does not necessarily mean the sunglasses will filter out the UV rays.
Although sunglasses offer some protection, they do not offer complete
protection. Some styles of frames do not prevent unfiltered rays from reaching
the eyes from the sides, top, and/or bottom of the glasses. Sunglasses also
provide some protection from dust and particles in the air. It is more important
for persons with light colored eyes to wear sunglasses for protection than
persons with dark eyes. The lighter the eye the more sensitive to direct light.
      When we talk about light in reference to sunglasses, three types of light
are important.

1. Direct Light—direct light is light that goes straight from the light source (like
   the sun) to your eyes. Too much direct light can wash out the details of your
   surroundings and make it almost painful to try to focus your vision on anything.
2. Reflected Light—Reflected light, usually in the form of glare, is light that has
   bounced off a reflective object to enter your eyes. Just like direct light,
   strong reflected light can make it difficult to perceive the details or directly
   view an object. Snow, water, glass, and white sand are all good reflectors.
3. Ambient Light—Ambient light is light that has bounced and scattered in many
   directions so that it does not seem to have a specific source. A good example
   of ambient light is the glow in the sky around a major city. It would be very
   hard to identify a single source of light for that glow. Ambient light is how
   you are able to see when there is no direct source of light.



Lens Colors

The color of the tint determines the parts of the light spectrum that are
absorbed by the lenses. Color doesn’t affect UV blocking. Different colors
produce specific results:

•   Gray—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.
•   Yellow or gold—Yellow or gold tints reduce the amount of blue light while
    allowing a larger percentage of other frequencies through. Since blue light
    tends to bounce and scatter off a lot of things, it can create a kind of glare
    known as blue haze. The yellow tint virtually eliminates the blue part of the
    spectrum and has the effect of making everything bright and sharp. That’s
    why snow glasses are usually yellow. This tint really distorts color perception,
    which makes it inappropriate for any activity that relies on accurate color.
•   Amber and brown—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 suggest that near-UV light frequencies such as blue
    and violet can contribute to the formation of cataracts over time.
•   Green—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—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.

       Lens color can be a dye in the lens or a coating on the lens. Color on coated
lenses is more likely than dyed lenses to scratch or wear off. Coated lenses can
be protected by the manufacturer through use of scratch –resistant layers.
Overall dyed lenses retain color longer.
       Darkness of a lens determines how much visible light will be let in. If
glasses are to be worn in very bright conditions such as for water sports a darker
lens is more practical. For everyday wear, a medium to light lens is usually
sufficient and may be more versatile. The main point is to match the amount of
tint to the purpose for which the glasses will be used.

Types of Lenses

•   Plain—Plain lenses are uniformly tinted throughout the lens and come in lots of
    different colors. The darkness of the lens has nothing to do with how well it
    blocks UV light, but it will make a difference in how much visible light gets
    seen. This may be important for eye comfort during prolonged time in bright
    sunlight.
•   Single gradient—Single gradient lenses are tinted darker at the top than at
    the bottom. They may be useful for tasks like driving, where the road is
    bright but the dashboard is dark. They are useful for places like a beach,
    where light is reflected up from the sand. The difference in tint causes
    lighting to change as the wearer’s head moves, which may be annoying to some
    wearers.
•   Double gradient– Double gradient lenses are tinted darker at the top and
    bottom, but lighter in the center. These are designed for sports such as
    sailing, skiing, and tennis, where light comes in from above and is also reflected
    from below, but the center of vision has less light coming in. There are not
    appropriate for driving, since they darken visibility of the dashboard controls.
    Like single gradient lenses, the difference in tint may be annoying to wearers.
•   Polarizing—Polarizing lenses are specifically designed to reduce reflected
    glare, such as sunlight bouncing off water or pavement. This makes them
    especially suited to water sports and driving.
•   Photosensitive– Photosensitive lenses darken and lighten in response to the
    amount of available light. These lenses have millions of molecules of
    substances, such as silver chloride or silver halide, embedded in them.
    Photosensitive lenses darken more quickly than they lighten. They also do not
    darken as quickly in hot weather as in cold. They will not darken much while
    driving, since the car shades out much of the direct UV light to which the
    lenses respond. Lenses that start out with a dark tint will be darker when
    they change tint. Some wearers may be bothered by the length of time the
    lenses take to change. In addition, some lenses “wear out” and fail to darken
    or lighten after a period of time
•   Flash– Flash lenses have a mirror like finish on one side of the lens. It may be
    silver, colored, or iridescent. The coatings add more to appearance than
    usefulness and can scratch easily.
•   Polarized—Polarized filters are most commonly made of a chemical film applied
    to a transparent plastic or glass surface. 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. 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.

Lens Material

       There are several types of lens material. CR-39 is a plastic made from hard
resin that meets optical quality standards. Polycarbonate is a synthetic plastic
material that has great strength and is very lightweight. These lenses tend to be
lighter and are more impact-resistant. Glass lenses are heavier but are more
resistant to scratches.

Quality

      Optical-quality polycarbonate and glass lenses are free of distortions, such
as blemishes or waves, and have evenly distributed color across each lens. For
most purposes, like going to the beach or driving, look for a tint that absorbs or
blocks 70% to 90% of light. Tints that offer less than 60% blockage are mainly
good for fashion since they offer only mild protection. Anti-reflective,
waterproof, mirror and scratch-resistant coatings improve the functionality of
the sunglasses but also add coast. Many of the more expensive sunglasses use
Specific technologies including polarization, tinting and anti-reflective coatings to
achieve increased clarity, better protection, higher contrast or to block certain
types of light.

Frames

       Normal frames similar to prescription eyeglass frames filter the light
coming through the lenses but offer no protection from ambient light, direct light
and glare from other angles. Wrap-around frames, larger lenses and special
sidereal attachments can keep this extra light from your eyes. The material used
to make the frames is often a huge factor in cost and durability. Most
inexpensive sunglasses use simple plastic or wire frames, while name-brand
sunglasses use high-strength, light-weight composite or metal frames. Also, the
better sunglasses usually have features like tension springs that connect the arms
to the face instead of just screws.

Labeling

The American National Standards Institute (ANSI), in cooperation with the U.S.
Food and Drug Administration and the Sunglass Association of America, has set up
a voluntary labeling system for sunglasses. Manufacturers may choose whether or
not they wish to use the labeling system. Sunglasses are regulated by the Food
and Drug Administration (FDA) as medical devices.

Recommended standards include:
• Sunglasses must block 99% of UVB light. A UVB-blocking sunglass is adequate
   to protect eyes in moderately bright sunlight like that found in low-altitude,
   urban areas.
• A UV-blocking sunglass blocks 99% of both UVA and UVB. A UV-blocking
   sunglass is adequate protection in very bright sunlight like that found in low-
   altitude snow areas and beaches. Such sunglasses reduce glare and increase
   visual comfort. The lenses should allow you to recognize traffic signals
   accurately.
• To protect eyes during prolonged daily use in extremely bright sunlight, like
   high-elevation snow areas and equatorial sand beaches, a UV-blocking sunglass
   should block 92 to 97% of visible light and have side shields. Goggles are also
   acceptable. Side shields are needed in extremely bright sunlight to prevent
   UV rays and light from being reflected into the eyes. These sunglasses limit a
   drivers ability to accurately recognize traffic signals. Side shields should not
       be worn when driving because they eliminate peripheral vision.
•   The only medical claims allowed on sunglasses are that they prevent cataracts
    and photo keratitis.

Tips

      Remember that the most important protection factor by far has to do with
how often you actually choose to wear your sunglasses. So you need to consider
ALL the factors that will influence your desire to keep them on your face.

•   It is essential to understand what “the right choice” means. It’s actually very
    simple. The “best” sunglass is the one which you will actually WANT to wear
    most of the time when outdoors, especially in the sun.
•   Don’t underestimate the importance of style. How we see ourselves and how
    we seek to enhance our appearance is for many the most important factor in
    maximizing actual use.
•   Fit and comfort are crucial. Take time to try on sunglasses and consider how
    they feel. They should be comfortable and secure. Just like trying a new pair
    of shoes, take the time to fully experience the fit. Remember, a high
    performing UV blocking lens does not protect if it’s on the dashboard, in your
    purse, or slipping down your nose.
•   Don’t forget to look through the lenses and let your eyes be the judge of how
    well you can see. If possible step outside and look at both light and dark
    areas. You want a lens that is dark enough to protect against glare and be
    comfortable in bright light, yet not so dark that it compromises your vision in
    low level light situations.
•   Remember, a major purpose of wearing sunglasses is glare reduction in normal
    sunlight activity. Sunglass lenses are impact resistant as required by FDA but
    they are not shatterproof.

Kids

       Children may not be as interested as adults are in the fashion aspect of
sunglasses. But because kids spend much more time than most adults do outdoors
and in direct sunlight, UV protection for the eyes is extra important.
       In fact, may experts believe our eyes get 80% of their total lifetime
exposure to the sun’s UV rays by age 18. Since excessive lifetime exposure to UV
radiation has been linked to the development of cataracts and other eye
problems, it’s never too early for kids to begin wearing good quality sunglasses
outdoors.
                                                 References

Beyond Fashion: Why You Gotta Wear Shades. http://newswise.com/articles/
view/540549

Children, Teens at Greater Risk Than Adults of Exposure to Damaging UV
Radiation. http://earthtimes.org/articles/show/children-teens-at-greater-
risk,384997.shtml

How Sunglasses Work. http://science,howstuffworks.com/sunglass.htm

Kids need sunglasses, too. http://consumerreports.org/cro/babies-kids/child-
safety/outdoors/sunglasses-for…

Sunglass savvy. http://consumerreports.org/cro/health-fitness/beauty-personal-
care/sunglass-savvy-705/ove…

Sunglasses. (1997-98). Consumer Decision Making Contest Study Guide.
University of Georgia Extension.

Sunglasses & You: Seeing Your Way Through the Confusion of Sunglass Selection.
http://sunglassassociaiton.com/trial/SunAndWe.html

Sunglasses for Kids. http://www.allaboutvision.com/sunglasses.kids.htm



Adapted by: Annette Cole, University of Tennessee Extension, Stewart County
2008.




The University of Tennessee Extension offers its programs to all eligible persons regardless of race, religion, color,
          national origin, sex, age, disability or veteran status and is an Equal Opportunity Employer.

				
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