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Selecting Sunglasses

Why do I need sunglasses?

To protect your eyes from dangerous ultraviolet rays, to reduce glare to a comfortable level, and to improve night vision. We have been is the sunglass business for 49 years, we have the experience to help you choose what is best for your specific uses.

What is ultraviolet light? 

Ultraviolet light (UV) is the invisible rays from sunlight that can harm your eyes. Cataract formation has been linked to UV light. UV light is what causes a lot of things to deteriorate, like tires, paint, etc.

What is infrared light?

It's the invisible rays from the sun that are made up mostly of heat waves. Infrared (IR) light has no known harmful affect on humans other than causing discomfort to your eyes, causes contact lenses to “dry out” faster.  IR light can be stopped only by glass sunglass lenses.

Light transmission levels of lenses

VLT = Visible Light Transmission, UV =  the Ultraviolet light and IR = Infrared light. On this website you will see us use these abbreviations to keep the length of copy as short as possible. We use light transmission as a standard measure, this is the amount of light that the lens will allow to pass through. Example; a lens with a VLT of 15% allows that much of the visible light to pass through the lens and reach your eye (it blocks 85% of the light).

If the sunglass provider does not offer visible, infrared and uv transmission levels, you have no way of knowing what you are buying, regardless of price. Price alone is no longer an indication of quality or protection level. Plastic lens tints are infinitely variable since most are tinted after they are made.

How can I determine what the VLT is on my own?

The levels we provide in these guides are pretty much useless if you have no way of deciding what is dark or light for you. Unfortunately, most of the sunglasses offered (including the most expensive) do not publish their UV, IR or Visible light transmission levels. The only guide we can offer for you to judge on your own is to find a pair of Ray-Ban© sunglasses with the G-15 GreyGreen lenses and look through them, they have had a VLT of 16% for over 40 years. The Randolph Engineering Military Issue glasses with the Neutral Grey lenses (Dark grey) also have a 16% VLT.

How do sunglasses help night vision?

If you subject your eyes to intense glare during the day, they will tend to “defend” themselves by trying to adapt to the bright light. This natural built-in defense will persist for several hours after the glare is gone, resulting in much reduced night vision. Studies have shown that night vision can be reduced by as much as 50% by this exposure. Wearing good sunglasses during the day will improve night vision considerably.

The military has known for decades that troops that are going to go on night operations need to prepare their eyes during the day by keeping them in very low light conditions by wearing dark glasses. This wiii increase their night vision adaptation time to a minimum. If you are a professional driver, pilot or involved in day/night operations, wearing a good pair of sunglasses during daylight hours will help you see a lot better at night.

What is the definition of a good sunglass?

It reduces visible glare to a comfortable level, eliminates most of the ultraviolet and infrared light, produces no distortion, transmits colors with little or no alteration, fits comfortably and is durable.

How do I choose the proper sunglass lens?

First, determine what you are going to use it for most of the time. If driving is your biggest use, then choose one for driving. Don't make the mistake of choosing a sunglass for something that you only occasionally do, like snow skiing or fishing. There are special lenses for all activities, if you can afford more than one sunglass, then choose the best ones for each specific activity. Remember, no one lens can do it all, you may need more than one.

How to select sunglass lenses

To provide full, day-long comfort, sunglasses should eliminate all of the problems that glare can present. Lenses of 15% to 30% visible light transmission seem to reduce glare sufficiently. The visible light transmission (VLT) is the amount of light the lens allows to pass through. A 15% transmission is dark, a 30% lens is lighter. Most high quality sunglasses with glass lenses will usually have visible light transmission levels of 15% to 20%. If your eyes are extra sensitive you might require darker tints, we can provide plastic lenses down to as low as 2% VLT, extremely dark.

Selecting the darkness (density) of the lenses

General purpose lenses that have VLT levels of 15% to 20% work best for people with "normal" light sessitivity. If you are going to spend a lot of time fishing, snow skiing or boating, you might get a darker lens, say around 8% to 12%.

If you have extra sensitive eyes, you could go down to 8%, or even less, but we normally don't recommend lenses darker than 8% unless you have a sensitivity problem. Some people with blue eyes may have a higher sensitivity and require the darker tints.

As you age, your eyes gradually lose their “light gathering ability”, especially after age of 50 or so, therefore you may not need sunglasses as dark, you can move up to the lighter lenses that have a VLT of 20 % to 30% or even lighter.

Selecting a lens with the correct VLT for you is the first step, next and also as important is selecting lenses that block ultraviolet (UV) light. Since UV light is one cause of cataracts, the lenses should block most of the UV. The UV light transmittance should be less than 5%. The other rays to consider is IR (infrared)—mostly heat waves, it is important to block IR if you wear contact lenses, or spend a lot of time in direct sunlight. Heat waves cause the eyes to “dry out”, thereby causing "scratchy eyes" and adding to discomfort. Only glass sunglass lenses block a lot of IR light.

Don't get lenses that are too dark. You can become addicted to dark lenses, and they can be dangerous when driving if you go from a sunshine area to a tunnel or heavily shaded area, you will be blinded temporarily if the lenses are too dark.

Don’t judge the density or darkness of the lenses for the first minute or two when you walk from inside a building to outside. The difference in light intensity is like 1000 to 1, and no lens will compensate for that much difference, your eyes will adapt after a minute or two.

Traffic light and color recognition is also important. Some cheap plastic lenses can severely distort colors. If you stick to Dark Grey, G-15 or Kontraster™ lenses made of glass, you won't have a problem with color distortion. If you have an occupation that requires precise color identification, use the Dark Grey (sometimes called the Neutral Grey lens), they are the most color neutral.

Read through our guide for specific recommendations on lenses for various uses.

How to choose a frame

Choosing a frame (for other than just looks) involves answering a couple of questions. First, are you “hard” on glasses? If you are, you might think about choosing Nylon, Randolph Engineering metal, Stainless Steel, Titanium, or Titanium Memory-metal frames, they are the most durable and will take a lot of abuse. If you take good care of glasses, you can choose any frame material you want. The least durable frames are the so-called “rimless” frames, since the "frame" is the very thin plastic lenses themselves, they tend to be very flimsy and will take no abuse at all. We will not install cable temples on rimless frames, as it will hasten their demise.

Frame nomenclature:

There are 2 main parts to frames, the frame front (part that the lenses go in) and the temples.

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Skull Temples are usually measured from the point where they attach to the frame to the very tip.

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Frame sizing: We measure frames in 2 ways, the old traditional way by measuring the width of one lens (called the lens size), and another way by measuring the overall width of the entire frame. We will usually always include the overall width of the frame in millimeters, this is measured for the total width of the frame from the outer edge of one wide to the outer edge of the other side.

 

How to determine your cable temple size 

If you are now wearing skull temples, and they fit well, see if you can determine what size they are. Sometimes it is stamped on the inside of one temple, you can measure it from the screw hole to the tip, or, if you have our printed catalog, all of the frames are illustrated full size, so you can lay your skull temples over the ones shown in the catalog.

Cable temples are also measured from screw hole to the tip, turns out they are usually 15mm longer than the skull temples. Example, if you wear a 140mm skull temple you would also wear a 140mm cable temple, even though the cables are 15mm longer at 155mm. The optical industry normally adds 15mm to temples to allow for the temple to wrap all around your ear, so a paid of Ray-Ban's advertised to have 140mm normal skull temples will require 155mm cables to fit the same way.

If your skull temples are this size. . .

Then you should get these cable temples

The actual size of these cables are

130mm

130mm

145mm

135mm

135mm

150mm

140mm

140mm

155mm

145mm

145mm

160mm

150mm

150mm

165mm

155mm

155mm

170mm

Frame fit is most important. If the frame can't be adjusted to fit your face, they will be uncomfortable to wear. Choose metal frames with nose pads that have adjustable arms (most good quality opthalmic frames have temples and nose pad arms that can be bent to fit your face), that way you can bend them to fit your nose and face. All the ophthalmic type metal frames that we sell can be adjusted.

The human head is distorted. New frames are normally very "square" mechanically. They will rarely fit correctly without adjustments.

1. Almost everyone has one ear lower than the other.

2. The ears are rarely the same distance from the nose.

3. The ears differ in their vertical position from person to person.

4. The eyes are not exactly on the same plane.

5. The nose is not quite centered between the eyes.

6. Noses come in a lot of different widths and shapes

7. Cheekbones come in a variety of positions and sizes.

All of this can result in frames that sits crooked on your face. So when you first put a nice "square frame" on your face, chances are real good that it won't fit right.

Temple adjustment: The temples can be adjusted up and down individually to straighten the frame horizontally on your face, this compensates for ears that are not level. You can bend the temples up or down to correct the horizontal position (nylon frames and many plastic frames can’t be bent to make this adjustment).

If temples on metal frames are too long, you can bend the tips down more to make them shorter to fit better, this adjustment will also keep the frames from sliding down your nose.

If the temples don't go down behind your ears where they belong, you can take some of the bend out to make them longer, or, you might need a different size temple. If you wear a helmet you might have to straighten the temples a lot so you can slip your glasses on under your helmet. 

Frame "Tilt" adjustment: If the bottom of the lenses are too far away or too close to the bottom of your face, you can bend both temples up and down to tilt the frame correctly on your face.

Nose Pad Arm adjustment: The nose pads can be adjusted to allow for crooked or offset noses, wide or narrow noses, and to position the frame in the correct position on your nose vertically. 

Frame size is important to everyone, but especially people who have prescription lenses. The smaller the frame size, the thinner and lighter the lenses will be. If you choose glass lenses, smaller frames will produce lighter lenses and add to your comfort.

Rimless frames used to be really popular, they look really good, but you must consider the extreme weakness of these frames. In a rimless frame, the lenses are the frame, and lenses are not real strong, so if you are not careful, you can expect some frame/lens problems with them.

Which sunglass lens is best

There are many lenses available for both general and specific uses. We are in the business of selling top quality, effective sunglasses. If you shop at local stores, and the merchandise is not marked with the visible light transmission (VLT) and filter characteristics of the lenses (amount of UV and IR filtered), you have no way of knowing what you are buying. We publish as much information as we can about all of our lenses and frames. Price is no longer an indication of quality, and has not been for quite a few years.

With all of the hype and marketing of so called “Brand” names, the consumer has almost no resource to check the quality of what they are buying. There are so many designer “name brands” now days, some named after dead people, animals, fictitious designers, children, things, cars, etc. that the consumer is left trying to decide on “brand”, when he should be taking a hard look at the merchandise itself to see if there is any value there. The suggestions here are based on our 49 years experience in this business.

Glass or Plastic lenses?

The first decision to make is the lens material. We'll give you all the pros and cons of all the lens materials.

GLASS lenses

Advantage: The color in glass lenses last forever and is very consistent between batches. Plastic tinted lenses can vary between batches, color fades as they age and sometimes need to be re-tinted at a later date.

Advantage: Glass lenses are optically superior and have several advantages over plastic lenses, the most important ones being higher scratch resistance, clearer vision and better filtration. About 80% of our sunglasses sold have glass lenses. Almost all of the better manufacturers use glass sun lenses for non-prescription glasses.

Advantage: Glass is much clearer that plastic (clear glass lenses have a VLT of about 95%, the VLT of plastic is about 85% at best). The better filtration comes from the fact that colored glass stops both infrared (IR)and ultraviolet (UV) light, and is more consistent in density and color. Objects always appear much sharper looking through glass sun lenses rather than plastic sun lenses.

Advantage: Glass lenses generally outlast several pair of plastic lenses because of superior scratch resistance. Glass lenses are also more chemical resistant than plastic, will not scratch as easy from improper cleaning.

Disadvantage: The downside to glass lenses is that they are heavier than plastic, especially when you graduate to the thicker prescription glasses, and even though they are heat treated and very impact-resistant, they are not as impact-resistant as polycarbonate plastic lenses. Another factor to consider for prescription glasses is the fact that glass prescription lenses are less than 3% of the overall market, so the selection and availability is getting worse by the day.

Disadvantage: Another problem with colored glass lenses is that for prescription use the uneven thickness of the prescription will cause the lenses to be thinner or thicker in areas, thus causing lighter and darker areas across the lenses. If your prescription is over 2.50 (under the sphere column) you might consider going to plastic. Also, glass lenses are becoming scarce, some glass lenses have disappeared completely in the last few years. Prescription Glass has dropped to under 3% of the prescription lenses sold, as the market for them continues to diminish, the prices are going to continue to rise, and the choice of glass will get smaller. On the other hand, the non-prescription glass lenses are about 80% of our sales.

 

Plastic lenses

The advantage plastic lenses offer (CR-39 especially) is that it can be tinted to any density from clear (VLT=100%) to opaque (VLT 5% or less), and anything in between, so they offer a wider selection of “darkness” as well as the availability of Top-gradient density tints, which are darker at the top and lighter near the bottom.

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Advantage: Plastic lenses cost much less than glass.

Advantage: Plastic lenses are lighter than glass lenses.

Disadvantage: Plastic lenses scratch easier than glass lenses.

Disadvantage: Plastic lenses shrink with age, if the frame is very thin (such as Ray-Ban metals and a lot of the thin fashion frames) the lenses can shrink enough to fall out of the frame.

Disadvantage: Tinted plastic lenses produce a phenomenon we call “red lenses”. When you hold your tinted lenses up to outside light, they appear whatever color they're tinted, if you hold them up to an incandescent lamp, they will appear red. Or, if  you look at yourself in a mirror under incandescent light, the lenses will also appear red. Without going through a lengthy explanation, suffice to say that you are looking at a filter, through a filter. This is normal for plastic lenses.

Disadvantage: Lower visual acuity; because matrix of glass lenses start out with a higher light transmission (about 95% or more), they are clearer than plastic lenses that generally have a light transmission of around 85% or less.

Disadvantage: Tinted plastic will lose some of their color after a while, they tend to get lighter, some turn to a kind of magenta color. Colored glass lenses keep their color forever.

The 4 kinds of plastic lenses

CR-39 plastic is the most popular lens material used for prescription lenses. It's light, easy to work with, can be tinted to any density, and is more scratch resistant than polycarbonate plastic.

Polycarbonate plastic is the material used on almost all cheap over-the-counter plastic sunglasses, and some very expensive one also, it has the highest impact-resistance and is used most often used for prescription safety lenses. It is softer than CR-39 plastic, so it scratches easier, and it can only be tinted to a medium density (about 35% VLT, except some non-prescription lenses have the color molded in, so can be a lot darker). This material is used in rimless frames. One advantage of Polycarbonate plastic is that it is lighter and a little thinner than CR-39 for the same prescription.

Trivex: Made by the same company that makes CR-39 lenses, this is the strongest lenses out there, they are used mostly used in rimless frames that are required to have holes drilled in them, and safety lenses.

Thin Plastic (high index) is high-density plastic that has a higher refractive index than regular CR-39. This means that lenses will be thinner using this material. If your prescription is over + or - 4.00 (under the sphere column), and you are using a large diameter frame, like a 60 eye size, using this material will make the lenses thinner and lighter. Most of today's frames are so small that there is not much of an advantage to this material, if you use smaller frames like eye size 48mm or so, you won't notice them being much thinner until you reach prescriptions of + or - 5.00 or more.

Which lens is best for specific uses

If you don't have time to read this guide, see our Sunglass Selection chart. Our recommendations are based on glass lenses. Here is a list of the most common uses for sunglasses.

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              Kontraster (B-15)                Dark Grey (Neutral Grey)         American Gray (G-15)

For General Purpose the Dark Grey, Kontraster and G-15 American Grey lenses all work well for all-around use. They all have visible light transmission (VLT) levels of about 16 to 17%, are dark enough to handle most glare. Polarized versions of these lenses will eliminate a little more glare by getting rid of some of the reflected glare off water or other flat surfaces.

For DRIVING, all of the general purpose lenses work well. Polarized lenses eliminate some of the reflected glare off the highway, trees, water, the hood and windshield that normal sunglass lenses only reduce. If price is not important, the polarized lenses work well for driving. However, the non-polarized Dark Grey, G-15 and Kontraster™ glass do what a sunglass is supposed to do, they dim the light and protect you from UV rays. The disadvantage of polarized lenses is that they "black-out" LCD displays that are found on a lot of speedometers, cell phones, radios, etc.

For FLYING the choice of our customers is the Kontraster™ glass (VLT=17%). It not only reduces glare, and blocks UV and IR light, but increases contrast. By filtering out more blue light it makes things look more vivid. Pilots like it because it reduces the effect of haze and smoke in the atmosphere to make it easier to spot other airplanes and to see ground check points easier. A second choice would be the Dark Grey or G-15 (LT=16%) glass, they do what a sunglass is supposed to do, they dim the light and protect you from UV and IR rays.

A note to pilots about polarized lenses. They should not be worn while flying. In fact, you can't even see through the windshield on most jets while wearing them because the windshields are laminated and cause severe color distortion. On the lighter airplanes you could wear them, but because the axis of the sunglasses are oriented at 90 degrees, as you bank the aircraft it causes the “world to change”, reflections off of water will come and go. Also, since they reduce the effects of reflected glare, it makes seeing other air traffic more difficult. Also, polarized lenses make LCD displays (such as used on GPS units, radios and LCD gauges) "black out", if you tilt your lenses about 90 degrees you can see them again.

For BOATING and FISHING the darker polarized lenses work best. The Dark Grey and the American Grey G-15 polarized (VLT=12%) are good for general purpose use on the water, the Kontraster™ polarized (VLT=15%) is better for fishing or any use where you are looking below the surface of the water to identify fish movement or other objects. The Kontraster™ polarized will make the bottom features underwater stand out better so you can see fish, rocks or grass easier. Also, remember, the Kontraster™ reduces the effect of haze, so you can spot buoys and landmarks easier. The downside to polarized lenses on boats is it makes it very difficult to read instruments that have LCD displays, the manufacturers put polarizers on the faces of these instrument that are aligned 90 degrees from the polarized sunglass lenses, so you'll have to tilt your head to read the LCD instruments, including cell phone and other digital displays. 

For SKIING the Dark Grey, American Grey G-15 (VLT=16%), Kontraster™ (LT=17%) and Rose Smoke lenses are the top choices. Don’t use polarized lenses, by eliminating reflected glare they mask ice patches on the slopes. On dull overcast days many skiers wear yellow lenses to increase contrast. At high altitudes the amount of UV light increases dramatically, whatever lens you choose, make sure it gets rid of most of the UV light. If safety is important to you, use polycarbonate plastic lenses, although they scratch easier, they are the more impact-resistant. The CR-39 plastic lenses can be tinted to any density from clear to opaque, so if you want extra dark lenses for skiing we can reduce the visible VLT to anything you want.

HUNTING and SHOOTING require protection first, which means that the lens size should cover your eyes well, and secondly, they should sharpen your vision as much as they can. If you are shooting or hunting under low light conditions, the yellow or amber lenses work best. They increase contrast to sharpen things up. If you are hunting in bright conditions, lenses with a lot of yellow or amber work best, like the Kontraster™. If you wear prescription glasses have them made CR-39 material so the lenses can be darkened to any density you want to cover any light condition. A lot of folks use the Changeable Grey lenses because they will automatically darken and lighten as light conditions charge. Some people also like the Serengeti Driver lenses for hunting and shooting.

For GOLF and TENNIS keeping track of the ball can best be accomplished with the Kontraster™ (LT=17%). Since it filters more blue light, it makes the balls stand out from both the blue sky and green background. Lately there has been some interest in Teal colored lenses for both of these sports, Teal is available in CR-39 plastic lenses as a tint. Just because the lenses are Teal colored don't mean that they are all created equal. The lenses we test mostly came up short, the only one that passed as a real Golf, Tennis or Clay-shooting filter was the one made by Randoloph Engineering for their shooting line.


For BACKPACKING and CYCLING any of the general purpose lenses will work fine, except for cycling, if you wear a full face shield do not use polarized lenses, as the face shield stress marks will show up and interfere with your vision. Some cyclist like the Changeable Grey lenses that self adjust to changing light conditions so they can use only one pair of glasses all day.  The changeable lenses work well for backpackers as well, except if you are going to be at very high altitudes where the changeable lenses do not get dark enough or filter UV light as well as the general purpose lenses solid tinted lenses.


If you wear CONTACT LENSES we've found that lenses that stop both UV and IR (infrared) light are the most comfortable. The IR light causes your contacts to “heat up” and dry out faster. Any of the general purpose colored lenses made of glass will work. This would be the glass lenses only, the Dark Grey, American Grey (G-15) or the Kontraster. None of the polarized lenses, glass or plastic, filter IR light very well.


COMPUTER CRT screens and FLOURESCENT lights can cause a low glare condition that is bothersome. One of the most effective ways of cutting this glare from your prescription lenses is to apply an anti-relfection coating (AR coating) to your lenses. This will eliminate the glare on your lenses. If the intensity of the light bothers you also, adding a very light “Softlight” tint will reduce the intensity of the light about 20% to a more comfortable level. So a light color tint and an AR coating are the best combo for this glare. Very light colors for computer use can be a light grey, light green, light brown or the most popular and best choice would be the light rose color. The tints are so light that you have to hold your glasses over a white piece of paper to see it, but it does help.


 

NIGHT DRIVING  glare bothers a lot of people. One of the best preventative measures for improving your night driving vision is to wear good sunglasses during the day, especially during the last few hours of daylight. This will make your dark adaptation time shorter and improve your night vision considerably. If you do this and you still have a problem with night driving glare, you might try putting an anti-reflection coating (AR coating) on your clear lenses, and add a light tint like  Yellow to cut the glare down. You can't darken glasses much for night time use, but the yellow lenses have a high VLT of around 75%, so it shouldn't interfere with your night vision. The ultimate night driving lens is the light yellow tint with an  AR coating. Note about AR coatings: AR coatings do nothing for outside glare coming through the lenses, all an Anti-Reflection coating does is remove the glare off the lenses themselves, they do not alter the glare you see, only the glare on the lens itself.


Medical problems can also require certain lenses. If your doctor prescribed certain lenses for you, call us to find out if we can help you. There are all kinds of lenses out there to help you with certain eye diseases.

So-called “old eyes” can make seeing under poor light difficult. As we age our eyes “wear out”, they require much more light to see well. If you are having difficulty reading at night, try putting brighter bulbs in your reading lamp, if you had 60 watt bulbs, try 100 watt+ bulbs. Correct reading lenses will also help.


 

GLASS LENS Descriptions 

DARK GREY or American Grey G-15 glass lenses have identical characteristics.  Dark Grey (like the Military issue) lenses are a blueish/grey color, the G-15 is Greyish/green in color (like the Ray-Ban). They both do the same thing, they lower the glare intensity to a comfortable level, provide UV and IR protection, and have a VLT of about 16%.  Available in non-prescription and prescription lenses. Used for general purpose use. The Dark Grey will not alter colors that you see.

KONTRASTER glass lenses are amber/brown in color, about the same color as an amber/brown beer bottle. VLT is about 17%. so they can be used for general purposes. With the high amber content of the lens it filters light a little differently than the other lenses. It filters more blue light, thereby increasing the contrast of what you see. Since it filters more blue light, things appear clearer, improves depth perception, and reduces the effects of haze and smoke and light fog (which is made up of scattered blue light).  

Pilots like this lens because it makes checkpoints easier to see, and spotting other air traffic is easier. Fishermen like this lens because it makes it easier to spot buoys and other water markers. 

People who live in climates that produce a lot of overcast but bright days like it because it “brightens up” your world, is less depressing than wearing grey lenses on those grey days. Skiers like it because it not only cuts through light fog and haze, but produces enough contrast to see moguls easier. If you are in to almost any kind of outdoor activity, you will find this lens to be the best choice by far. Although it appears to be lighter in tint than the Dark Grey or G-15, the VLT is only 1% more. 

POLARIZED GLASS lenses eliminate reflected glare that other lenses on reduce. Because these lenses are different, we have a whole section in this guide devoted to them, click on Polarized Lenses.

 

MIRRORED GLASS LENSESused to be popular when they could be applied to make really dark lenses, now because of legal reasons most of the coating labs will offer only flash mirrors that reduce the VLT to about 11%. A flash mirror on a  Dark Grey, G-15 or Kontraster glass applied to the front surface will reduce the overall VLT of glass lenses from 17% down to about 10 to 12%. The exact VLT applied in batches is very unpredictable, so the above figures are about as close as we can estimate. The downside to mirrored lenses is that they can cause severe sunburns on your nose and face due to them reflecting the sunlight, this doubles the amount of UV on your nose and the front of your face. They are used today mostly for fashion not function, except in the case for certain eye disease where the VLT must be made extremely low, like 2%.

 

CHANGEABLE  lenses

Changeable lenses such as the Changeable Grey, Changeable Brown, Photogrey Thin & Dark, Serengeti Driver and Transitions get darker and lighter depending on how much ultraviolet light is striking them. In the plastic version they are called “Transitions™” (this is a trademark name). We will refer to them all as changeable lenses, they all have very similar characteristics. 

 

How changeable lenses work

 To darken, most of these must have ultraviolet light from the sun striking them directly. Most won't darken inside a car or sitting behind windows. When the source of sunlight/ultraviolet light is removed, they go back to their light state. Some will darken as much as to 13% in cold bright conditions, and lighten to nearly clear at 86% in the dark.

 

Several things affect the darkening/lightening process:

1. The most important condition that affects lightening and darkening for most of these is ultraviolet light, the lenses must have uv light shining directly on them to darken.

2.  The length of time they are exposed to uv light will determine how dark they get, they usually reach around 50% of their darkness after a minute or two, then will continue to darken for about 10 more minutes. Some of the newer lenses darken and lighten faster.

3.  The temperature of the lenses have an affect on the darkness, they darken more in very cold weather, they don't darken as much in hot weather. Most of them work better at temperatures in the 60 degree and below range. Some of the newer plastic changeable lenses are not affected by temperature.

4.  The thickness of the lens also affects how fast glass lenses darken/lighten, and how much they change. Thicker glass lenses get darker than thin ones and do not lighten as much. Plastic changeable lenses such as the Transitions™ or Sunsensors™ are not affected by lens thickness since the changeable material is a layer on the front of the lenses.

5.  The glass lenses have a built in memory, that is, when you first get them they will be slow to change, as you wear them more and more they will change a little quicker. If you put them in a drawer for a period of time they will revert back to the “new” condition  and you'll have to start the process all over. The plastic changeable lenses change faster and are less affected by memory.
 

Changeable lens availability


CHANGEABLE GREY or CHANGEABLE BROWN glass will lighten to about 85% inside (almost clear), and darken to about 25% outside (subject to the 5 conditions listed earlier). Expect them to not get this dark in the summer time, the maximum darkness in the summertime will be more like 35% or so. Can be worn indoors or at night. Available in non-prescription and prescription lenses. The Corning name for these glass lenses is Photogrey Extra and Photobrown extra.

 

CHANGEABLE PLASTIC lenses are sold as Transitions™, Sunsensors™, Drivewear™, and under many other brand names. They are available in Changeable Grey (all the same characteristics as the Changeable Grey glass lenses described earlier, except they change a little faster). The actual VLT varies considerable from brand to brand.

 

Plastic tinted lenses

 

Plastic lenses offer the same colors and performance as the glass (Grey, Green, G-15, Kontraster, Teal, Yellow, etc.) except that they do not filter much IR light. The nice thing about plastic lenses is that they can be tinted to any density (VLT) you want from clear to nearly opaque, and if the color or density is not right for you, we can remove some of the color to make them lighter or add color to make them darker.

 

GRADIENT DENSITY plastic lenses are really popular because we can tint the lenses darker at the top to filter out more sunlight coming for high angles, make them lighter in the center for normal use, and the bottom can be lighter so you can see the speedometer or read maps easier. They are very flexible as far as density goes, we can make them just about any density you want (in addition to the ones published as dark, medium or light top-gradients). Available in non-prescription and prescriptions lenses.


YELLOW lenses are very lightly tinted lenses used to increase contrast. VLT is usually 70% or so. They are not sun lenses, although they do stop the UV light, the VLT is too high for use as a sun lens. Also used for night driving to reduce headlight glare. Available in non-prescription and prescriptions lenses.

 

Dark Amber polycarbonate lenses are available from our lab. They are for people with light sensitivity problems, historically blue eyed blond haired people have higher sensitivity than normal. The Dark Amber lens has a VLT of only 7%, knocks out 93% of the incoming light. Was originally designed and used for Arctic expeditions, mountain climbing, or use in extreme glare for long periods of time. We have only a limited supply of these available in a few of our frames.

 

POLARIZING LENSES

 

What is a Polarizing lens, how is it made? The illustration below shows a cut away drawing of the 3 piece laminated polarizing lens, The outside and inside of the lens is glass or plastic, the polarizing material itself (which is a very thin “Saran Wrap” like tinted plastic) is sandwiched in betweenPolarized_lens_cutaway.jpg the rigid front and back lenses.

 

So all of the color and filtration qualities of the lens is in the thin plastic material, the glass or plastic outer lenses are clear. This is what makes good polarizing lenses so expensive, it is like buying 3 lenses.

 

 

What is the  main advantages of polarized lenses?

Polarizing lenses eliminate some reflected glare that other non-polarized  lenses only reduce. The two key words here is eliminate and reflected

If you defined a polarizing lens you could say that it eliminates 100% of the reflected glare coming off a flat horizontal surface at an angle of 52 degrees.  The polarizing action diminishes as the angle of the reflected glare decreases or increases from 52 degrees. This means that if you are standing at the edge of a swimming pool looking down at the water, you will be able to see under water glare- free at an angle of 52 degrees, as you look farther out into the pool you will begin to see glare, the further you look the more reflected glare you will see until the polarizer becomes ineffective.

 

Advantages of polarizing lenses:

1. Eliminates some of the reflected glare coming off the dashboard of your car.

2. Eliminates some of the glare reflected off the inside of the windshield.

3. Eliminates some of the reflected glare from the surface of the road.

4. Eliminates some of the reflected glare coming off the windows of other cars.

5. Eliminates some of the reflected glare coming off trees, leaves and grass.

6. Eliminates some of the reflected glare coming off the surface of the water.

7. Eliminates some of the reflected glare coming from haze.


Disadvantage of polarizing lenses:

1. For driving or skiing they mask ice patches by eliminating the surface glare used to identify ice on flat surfaces. Will also darken LCD displays in cell phones, radio displays, GPS displays, Speedometers, etc.

2. For flying they cannot be used in airplanes with thick laminated windshields, like on large airplanes, you can’t see through the windshield because of the stress caused by the lamination's on thick glass.

3. For flying it masks the reflections coming off other air traffic, making it harder to spot other airplanes. Will also mask LCD displays like GPS receivers, etc., making them impossible to read.

4. For motorcycle riding or anytime you wear a helmet with a face shield, it shows the stress in the curved plastic shields and causes you to see blue spots on the shield.

5. For boating, while the polarizer works well for eliminating reflected glare off the water, it will mask LCD displays found on marine instruments, making them hard to read unless you tilt your head sideways.

6. Glass polarized lenses can not be tempered and are not a hard as regular glass lenses, so they are easy to break.

 

Don’t forget about what makes a good sunglass lens, it’s ability to reduce glare to a comfortable level, and eliminate UV  light. The polarizer goes one step forward by eliminating some of the reflected glare while reducing the direct glare, but it goes one step backward by not eliminating as much IR light. 

So even though it allows you to see underwater if the water is clear, it does not eliminate the IR rays that add to day-long discomfort caused by excessive heat reaching your eye. The comfort of unpolarized solid colored glass sunlens (such as the Dark Grey, American Grey (G-15), Kontraster™ and Natural Green) stops IR light and let’s you see the LCD instruments on your boat, and provides day-long comfort that polarized or plastic lenses can not achieve.


 

Question: I noticed that you keep saying ‘some’ reflected glare, doesn't the polarizing lens eliminate all the reflected glare?

Answer: No, polarizing lenses only eliminate all of the reflected glare reaching your eyes from an angle of about 52 degrees. As the angle of the reflected glare decreases or increases—the amount of reflected glare that is eliminated is reduced. 

 To put it simply, if you were standing in front of a building (like the top illustration shows) with a polarized lens, you would see the reflections. In the lower picture with polarized lens, most of the reflection is gone and you can see through the window. Most of the glare close to you is eliminated, but as you look farther away, you still see some surface glare, that’s because polarizing lenses are only 100% effective at eliminating the glare being reflected from the surface at the 52 degree angle, as the angle of reflected glare keeps increasing until somewhere around 80 degrees it ceases to eliminate the reflected glare. 


Question: Glass polarized lenses are too expensive, what protection will I lose by buying the Dark Gray, G-15 or Kontraster® lenses instead? 

Answer: None. If you look at the lens transmission chart you'll see that non-polarized glass lenses are superior to polarized glass, they block the UV as well or better, they give you IR (infrared protection) which the polarizing lenses do not, they have a higher clarity than polarized lenses, and the impact-resistance is much greater because glass polarized lenses can't be made impact-resistant, therefore the are much more fragile. The only thing non-polarized glass lens won't do is eliminate some of the reflectedglare. Clearly, the glass non-polarized lenses are superior light filters.
 

Polarized lens availability


 GLASS polarized lenses are more scratch-resistant than plastic ones, they are available in two or three colors, the Dark Grey (which is usually an American Grey (G-15) which has some green in it), and the Kontraster™ (amber-brown color). The reason the Dark Grey lenses have a green tint added is to keep the lenses from turning a magenta color as they age. The polarizer in all polarized lenses use a saran-wrap like plastic sandwiched between two pieces of clear glass as the filter, this is where all the color and filtration takes place, the glass is used to hold the polarizer rigidly in place and protect it. Glass polarized lenses are available in prescriptions and non-prescriptions. Glass polarized lenses are not impact-resistant like our other glass lenses, to temper lenses and make them impact-resistant you must heat the lenses to 1200 degrees, this would melt the plastic polarizer sandwiched between the two glass lenses. So if you are going to use the polarized lenses where there is any danger of flying objects or other hazards striking the lenses, you might consider the CR-39 or Polycarbonate plastic lenses, or just use non-polarized impact-resistant glass lenses.
 

PLASTIC polarizing lenses (CR-39 or Polycarbonate) are lighter and more impact-resistant than glass. Non-prescription ophthalmic plastic polarizing lenses are 2.2mm thick (cheap plastic polarizing lenses are less that 1mm thick made of easily scratched acrylic plastic).  

The CR-39 plastic polarizing lenses offer excellent optical quality, they have a fairly hard surface to resist scratching, lightweight, and are more impact-resistant than glass polarizing lenses. They are available in Dark Grey, American Grey/green (g-15) or Kontraster™ colors, in both non-prescription or prescription.

Polycarbonate polarizing lenses are the most impact-resistant, preferred by people in fast moving outdoor sports such as fishing, playing ball, etc. The downside is that they scratch easily, so you will need to clean them carefully.

 

More lens choices: As technology advances, more and more lenses are showing up, most of them are derived from lenses we have already mentioned. Since sunglass marketing now involves a lot of hype, some claims are just outright lies, it's the consumer beware. A high priced sunglass does not mean a better sunglass, it is just a high priced sunglass.....

If you have a special need for lenses other than those listed above, drop us an email and describe what you need the lenses for, although we are semi-retired we can still help you.