What You Should Know About Sunglasses

What You Should Know About Sunglasses

JAMES R. GREGG, O.D.

PUTTING ON just any pair of sunglasses for motorcycling is about as logical as installing a mini-motor on a maxi-frame. Yet some cyclists do just that—wear sunglasses for every seeing need with little idea of whether they are good or not.

There is a huge difference in sunglasses. Wearing some of them is worse than none at all. Some are excellent for certain environments but inadequate, even dangerous, in others. The whole matter of tinted plastic goggles and face shields which motorcyclists use is a scientific no man’s land.

How much you need glare protection depends partly on the amount of time you spend outdoors. If you work in an office or factory and ride only on weekends, the bright sun will probably bother you a great deal. People who work outdoors, on the other hand, tend to adapt to high brightness. There are also individual differences in sensitivity to glare, depending upon pupil size and the amount of pigment in the eye.

Exposure to glare is terrific when riding. Pavement reflects a tremendous amount of light. Even trail riding is done in brightness thousands of times greater than that found indoors. If you frown or squint, or are annoyed by glare in any way, try sunglasses—the right ones. If you feel comfortable with them, use them for cycling.

Headache or fatigue can slash driving efficiency and dampen the fun as well. Glare can mask a hole in the road, cause errors in judging speed and distance. Safety is a dividend of wearing proper glare protection.

A hat or helmet with a bill helps cut the terrific brightness from overhead. But on most driving surfaces, reflected light should be softened for your eyes. There are two choices, either glasses or a face shield with a tint. In either case, you need to know some facts.

Wearing a glare protective device also shields the eyes from potentially harmful rays of the sun. These in excessive amounts can damage the tissues of the eye. Lesser amounts can create mild irritations and discomfort. There is little danger from a short time in the sun, even all day long, if it is infrequent. But the person outside a great deal could possibly be adversely affected.

Some experts believe that cataracts develop in the lens of the eye if it receives too many rays of certain types. This does not mean that wearing sunglasses guarantees you will not get cataracts, or that you will be afflicted with them if you don’t. It is not so simple. But the ideal sunlens should absorb wave lengths that have potentially dangerous properties.

Good sunlenses are made to absorb the invisible rays, which shoddy lenses probably fail to do. There is no way you can tell if a lens filters out the unwanted rays by looking at it. You must rely on the scientific data provided by the manufacturer, which is available for quality materials.

Wearing sunglasses in the bright sun will help you to see better at night. The rate and level of dark adaptation is increased if the visual cells are protected from too much visible light during the day. By use of very dark lenses, the improvement may be as much as tenfold. For driving on well lighted streets, the gain in night vision is not very important; however, out on the highway it could be an added safety factor.

Take sunglasses off at dusk. Never wear them at night. Any tinted lens, including yellow lenses, actually reduces the amount of available light. The Highway Research Board of the National Academy of Sciences reports that no tint in goggles or windshields has ever been proven helpful at night.

The only kind of a tinted lens that has some value at night is the Nite-Site Lens designed by a Colorado optometrist, Dr. Wendell Bryan. The right side of the lens is clear, the left side shades gradually into a medium green tint. The colored area of the lens is used to shield the eyes from bright headlights on the left side. When there is no glare, the wearer looks through the clear side.

The Nite-Site Lens is of no value in the city when light comes from all sides. On the open highway with glare from the lights of opposing traffic at night, it appears to have some advantage. But for general driving, no tint of any kind should be used. This goes for face shields, goggles, or anything worn in front of the eyes.

What properties should a good sunlens have? Since the main purpose is to cut the overbrightness, the degree of darkness is most important. Lenses should absorb the extra light not useful for visibility. This does not mean that any dark lens makes a good sunglass, however.

Data on the percentage of white light absorbed is supplied by the manufacturers of quality lenses, which is not the case for inferior ones. That’s one way of judging a lens; if you can’t find out its light transmission factor, the manufacturer doesn’t know or care. Ask for that information when you purchase sunglasses or plastic shields.

Exactly how dense lenses should be depends upon where you use them. On highways and tracks, desert and beach or in a brilliant sun, use a very dark lens, with 85to 90-percent absorption. For field and ground driving areas, 60 to 75 percent will do. During twilight hours and on overcast days, a lens with 30 to 50 percent absorption may be plenty.

More than one pair? Ideally, yes, and you should have lenses of different densities to deal with the varying brightness conditions a motorcyclist faces. Next best alternative, though, is to select a lens suited to your most common need, and learn to compensate or get along without it in other situations.

You can make a rough judgment about density by looking through the lenses in average outdoor brilliance. Give your eyes at least five minutes to adjust before you make a decision. The lenses should noticeably reduce glare and feel comfortable, yet not restrict how clearly you see.

1.) Photochromie lenses which darken to 45 percent transmission in sunlight. Good for some purposes if brightness is not too severe or prolonged. Makes a good second pair along with sunglasses of greater density.

2.) Plastic frames are good looking, can be very comfortable and practical, provided they curve to browline to reduce peripheral glare and fit snugly. The drawback is that wide temples may block side view.

Face-form, high quality goggles with gold■' filled rim have safety lenses, neutral gray color, temples to hold securely in place and are comfortable to wear.

4.) Very large goggles in a light green. Depending upon individual features, they will provide the widest coverage of any lens, and they have a sweat bar so the top of the frame can fit close to the forehead. Good for medium bright days but not dark enough when sun glare is at the maximum. (Gregg)

5.) Plastic polaroid clip-on. Can be used to fit over prescription glasses but not generally recommended for motorcycling, as they are small.

6.) Plastic lenses in bifocals. Lightweight and safe, good for working around machines and equipment when glare protection is not needed. Though temples are plastic, they are long enough to fit well.

Just as important as how much light is absorbed by a sunlens is what kind. It takes a spectrophotometer to determine the absorption of each wavelength. This is important in judging the value of the lens. Absorption curves are available for good sunlenses, which is another reason for getting only the finest.

The best color is a neutral one, such as grey or smoke. A certain grey-green is also good. These lenses transmit the rays most useful in seeing, absorb those which help very little, and do not upset the normal balance of objects seen through them.

Red, orange, yellow, purple, blue, and bright colors are unsuitable as sunlenses. The deeper the color, the more restrictive its spectral transmission and the more it upsets the eye’s normal performance. You want none of that for cycling, so stay away from mod colors, whether delicate tints or splashy hues.

Don’t wear the cosmetic colors or pastels so much in use today. They are not sunglasses. Many absorb only 10 to 25 percent of the light. Worn at night or indoors, they cut down visibility.

What about polaroid lenses? The best ones are laminated lenses, which have a sheet of polaroid plastic sandwiched between two layers of glass. The polaroid helps block reflected glare. The glass carries the tint to reduce brightness and is treated to absorb the harmful radiations. All prescription polaroids are made this way.

Plastic polaroid sunglasses without the laminated glass are subject to the same defects as any plastic. Color must be added to the plastic, as many are too light, but there is no doubt of Polaroid’s ability to cut reflected light dramatically in some situations. However, tilting the head changes the orientation of the polarizing factor and can let reflected glare get through.

Lens coating can also be used to reduce the amount of light entering the eye. Coating is actually a very thin metallic layer applied to the lens surface. The density of the coating controls the amount of light reduction, and its color determines which wavelengths are blocked. By a combination of color and density, most any kind of selective light transmission is possible with coating, which can be added to prescription lenses.

Coating reflects light and can be used to make the so-called “mirror” lenses. A heavier density on the top of the lens with shading lighter at the bottom is excellent for cutting glare of the sky maximally, yet provides good visibility on the road, since less light is blocked by the lower part of the lens. This might be a good choice for a motorcyclist who does not use headgear with a visor.

Recently a photochromie glass has been developed which automatically adjusts to the amount of light. Outdoors the lens darkens, inside it clears, thus making it useful over a considerable range of brightness. It is available in neutral gray and in prescription lenses, including bifocals.

Actually the photochromie lens is not a sunglass and the manufacturers do not claim so. Depending upon temperature and amount of sunlight, the lenses at maximum will absorb 50 to 60 percent of the light, not enough to put it in the true sunglass range. Still, for some people who don’t need a dark lens or don’t want to bother with two pair, it is very useful. Its speed of adjustment is generally adequate and the process does not seem to create any fatigue or deterioration.

The photochromie lens can be made more useful for cycling by applying a very light coating to the back surface. Such a lens absorbs only 30 to 40 percent in its lightest phase, yet blocks out 70 to 80 percent at maximum density. Thus, it can produce the absorption ratios most needed during the day.

Consult your optometrist about the photochromie lens, as coatings are added only on special order. Be sure the coating is not too dark or the variability range will become too compressed. It should be mentioned that there is a bad feature: the lens won’t work inside a car, boat or plane since it depends upon ultraviolet light to make its change, and this is filtered out by windows.

What has been said about tints applies to plastic as well as glass. Unfortunately, the plastic used in face masks and goggles for cyclists may not be good quality. It can be loaded with imperfections and can be scratched easily. The cheaper the price, the more likely this will be the case.

The tint in good optical plastic can be controlled, but it must be manufactured very carefully. The shields and goggle lenses in various colors generally have unknown light filtering properties, and the color often is not uniform and may fade with much exposure to light.

The best bet is to get good sunglasses, preferably in a goggle shape. Using a clear plastic face shield over the sunglasses gives maximum flexibility and the best in glare protection and face coverage as well. Be very wary of colored plastic shields and interchangeable goggle lenses.

As many sunglasses are useless because of inferior frames as because of imperfect lenses. Good frames generally carry first-rate lenses, but there are some sad exceptions. The reverse is also generally true: quality lenses are not sold in shoddy frames. But whatever kind of lenses you have, the frame must be dependable and fit well, or they will do you little good.

Cheap plastic frames can look practical but are seldom durable. Look carefully at the finish of the plastic to see if it is smooth, uniform, and neatly done. Inspect the hinges; they should be made of strong metal and be well machined. Compare the workmanship on a fine prescription frame and you’ll find a big difference.

Metal frames can fool you. Some metal is soft and will not hold shape, and consequently may corrode and break. Metal should be strong yet slightly flexible. Aluminum makes good frames if manufactured properly. The top of the line is gold filled material.

Just passable sunglasses may cost as little as $5, while $15 to $20 is reasonable for moderately good ones. Up to $30 to $40 for the finest is not out of line for the wrap-around goggle type best for the cyclist. The price partly depends upon how much service you get with them. This can account for the difference between a store price and what the professional man charges. It’s worth it.

Frame fit is vital to good sunglass performance. If the bridge is too small, it not only pinches but the lenses will set too far from the face. Short temples hurt; long ones let the frame slide down. Better sunglasses are available in various dimensions, selected for you.

Few frames of any style will be comfortable without adjustments. This is a big reason for not buying sunglasses over the counter; besides, it is tough to determine quality at supermarkets and gas stations. Automotive stores don’t provide adjustments even though they sometimes carry sunglasses made by reputable companies.

But the best reason of all for getting the finest in sunglasses is that your vision is so important.