Lens Materials
Lens Materials
Lens Coatings & Treatments
Lens Materials:
Polycarbonate:
Polycarbonate is virtually unbreakable, and it is used exclusively by many of the world's finest sports glasses manufacturers. It is thinner, lighter, and stronger than glass. What's more, polycarbonate lenses can survive a 12-gauge shotgun blast from 10 yards away. (Warning!: If you try this at home, take the glasses off first.)
Polycarbonate naturally blocks almost all of the sun's harmful UV rays. No coatings are required to block UV rays on a polycarbonate lens, so don't let anyone sell you this option.
The strength of polycarbonate is partially derived from its flexibility. It is not brittle and will not shatter. This strength also contributes to its main weakness. Because polycarbonate is so flexible, it is also easily scratched. New lens coatings and hardeners have significantly improved polycarbonate's durability, but choosing a polycarbonate lens still requires an informed consumer. Quality lens treatments match the refractive index of the lens material and allow light to pass through the coating at the same speed as the lens. If light passes through the lens coating and the lens at two different speeds, vision will be blurred.
Every lens we offer is manufactured to improve vision. Our customers are never at risk of getting stuck with substandard lenses or coatings.
Trivex:
Trivex is a new lens material that is quickly becoming the best thing that has ever happened to sports eyewear. Originally developed by the US military as an improvement over poltcarbonate, Trivex is stronger, lighter and optically superior to polycarbonate. Most importantly for sports applications, Trivex minimizes distortion called "chromatic aberration", which is distortion that occurs when objects are viewed away from the optical center.
Chromatic aberration is measured by "Abbe value." In prescription eyewear, a higher Abbe value indicates less distortion as you look away from the center of the lens. Trivex has an Abbe value of about 45, while polycarbonate has a value of about 30.
Trivex naturally blocks 100% of the sun's harmful UV rays, similar to polycarbonate. Trivex has better scratch resistance than polycarbonate.
Trivex is a relatively new lens material (available since 2003). It is still not offered by most manufacturers as a standard lens choice. We offer Trivex as an option on all of our prescription lenses. Trivex is usually about $25 to $40 more expensive than polycarbonate. All Kaenon Polarized sunglasses, prescription or not, have the Kaenon SR-91 lenses. The SR-91 lens material is very similar to Trivex.
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| CR-39 Plastic | Polycarbonate | Trivex |
Important note about scratched lenses:
If you scratch a polycarbonate or Trivex lens, you must choose one of two options. If you bought the glasses from us, send them back. We can usually replace the lens. If you can't replace the lens, THROW THEM AWAY! Polycarbonate and Trivex have amazing strength, until they are scratched. Once they are "scored" they lose their ability to protect your eyes. This is analogous to a carpenter using a razor knife to scratch, or score, a vinyl floor tile. As soon as he pops the tile over a straight edge, it will easily break along the scratch. Polycarbonate and Trivex will respond in a similar manner if a scratched lens receives an impact.
These are the two strongest lens materials in existence, but they are still not indestructible. Of the two, Trivex is stronger and more scratch resistant.
Glass:
Glass lenses provide excellent scratch resistance and clarity. They are also about 40% heavier than polycarbonate or Trivex. Unfortunately, glass is easier to shatter, and it is not available with Free Form lens surfacing. If impact could be an issue, glass lenses are a poor choice. Serengeti makes some impressive driving glasses with glass lenses, but none of our action-sport glasses come with glass lenses.
CR-39 Plastic:
CR-39 is the most frequently used lens material in prescription eyewear. It is the least expensive, and it works fine in environments that are isolated from sports related impact. For this reason, we hardly ever use it. CR-39 lenses are fine for driving a car, lounging on a beach, or when used in a prescription insert that is mounted behind a polycarbonate lens. But if you are an active participant in any sporting event you need a quality polycarbonate or Trivex lens in front of your eyes.
SR-91:
SR-91® is an awesome new polarized lens, and it is the perfect lens material for any sports eyewear. SR-91 polarization technology makes this lens exceptionally crisp and clear. The lens material is very similar to Trivex, and the polarization technology is very impressive. Kaenon Polarized, the sunglasses manufacturer, has the patent on SR-91. This lens material is featured in every one of their sunglasses, and every one of their polarized sunglasses. All SR-91 lenses are polarized to eliminate glare, and they block 100% of UV rays and Blue Light.
When we first heard about the strength and clarity of SR-91 we were a little skeptical. So at a recent eyewear trade show in New York we borrowed an SR-91 lens blank and took it to a Drop-Ball chamber used to test lenses for ANSI compliance. The normal 5/8-inch steel ball did nothing to the lens, so we put in a 4-inch solid steel ball bearing and dropped it 5 feet onto the lens. We wanted to see if the lens would shatter into sharp pieces, or just split apart. Not only did the lens stay intact, there was not a single scratch on it. We have never seen a lens respond this well to a Drop-Ball test. We are now big fans of the new SR-91 lens material.
The limitations of SR-91 include availability and price. The range of prescriptions blanks available is not as great as other materials that have been on the market for years. Currently SR-91 prescription lenses are available from -3.00 to +5.00. And as you would expect, this new, sharper lens material costs more than traditional lenses. Single vision prescription lenses are about 30% more. Progressive SR-91 lenses are about 75% more expensive than polycarbonate. It takes about 2-weeks for us to process prescription SR-91 orders. Other lenses take 2 - 5 days. But if sharp, glare-free vision is a priority nothing is a better value than SR-91 lenses.
We can put SR-91 prescription lenses in almost any frame you choose, regardless of who the manufacturer is. Call us for pricing if you do not see this option listed.
How can other on-line retailers charge under $75.00 for prescription sports lenses?
This is a function of both the lens material and the surfacing design.
The cheaper Rx lenses that you find on-line are usually made of CR-39. This is a breakable plastic material that should never be used in sports eyewear. Most frames from Wiley-X, Panoptx 7-Eye and Rec Specs have ANSI Z-87, or just “Z87” printed on the frame. This indicates that the frame has passed their safety testing, and it is not legal to put a lens in this frame that does not meet this same standard. The only two lens materials that meet this standard are polycarbonate or Trivex (also called NXT). In our opinion, putting a plastic lens in sports or motorcycle eyewear displays a reckless disregard for human life and is just a law suit waiting to happen.
Structural integrity is not the only problem with these cheap lenses. We use a digital surfacing design to give the best possible vision throughout the entire lens. Even when patients choose to avoid the additional expense of a digital lens we use a de-centering technique on wrap style lenses to minimize distortion. The optics in a cheaper lens are visibly inferior.
If you just can’t resist one of these extra cheap on-line prescription offers, you should make sure you’re an informed consumer. Ask the merchant what the lens will be made out of, whether they can offer free form lens surfacing, and if the finished product will meet the minimum ANSI safety standards.
Lens Treatments and Coatings:
Polarization:
Polarization is not a coating placed on the outside of the lens. It is a thin layer of iodine crystals arranged in vertical rows and sandwiched into the middle of a lens.
Although it may seem a bit feeble to compare this lens to microscopic mini blinds, that's really the easiest way to illustrate how polarization works. Light can pass straight through these crystals, but glare is completely blocked
Polarized lenses are absolutely the best way to eliminate glare. Coatings can be added to the surface of a lens to reduce glare, but these coatings affect all light, not just glare. A polarized lens will dramatically improve vision on sunny days near water, snow, or roadways. Eliminating glare on water can even help you see below the surface.
The additional protection of polarized lenses is also important for refractive surgery patients and pre or post-op cataract surgery patients. Anyone on UV sensitizing medications such as insulin or hormone replacements will also benefit greatly from polarized lenses.
Polarized lenses are the greatest use of technology in the optical industry. But there are some limitations and even more myths that surround this material. If you're a pilot, you probably already know that polarized lenses can make some LED instrumentation invisible. Most glass cockpits are not affected. (We recommend the Serengeti Drivers Gradient lens for pilots.) Skiers love polarized lenses in bright sunny conditions on fresh powder, but alleged experts have been telling us for years that icy or crusty spots could be harder to see. We tested this theory and found it to be blatantly false. It is a refreshing change to see a few manufacturers like Native Ski Goggles and Panoptx finally reject these old myths and offer polarized ski eyewear.
Lastly, golfers often believe that polarization is not needed on a golf course because grass and trees don’t produce glare. The glare in wide-open sunny places is actually caused by the sun, not objects on the ground. To illustrate how significant this is we often recommend that golfers compare their favorite golfing glasses to the Kaenon Kore with the polarized Copper-12 or Copper-28 lens. If their vision is not twice as sharp with the Kaenon lens, they can simply send the glasses back. We ship them at no charge, and there are no restocking fees.
Anti-Reflective (AR) Coatings:
Typically, about 8% of the light that hits a lens is reflected off. AR coatings allow much more of the light to pass through to your eye. Although it may seem a little oxymoronic to put an AR coating on sunglasses, there are at least a couple good reasons to do it.
AR coatings on sunglasses have the most benefit on the back of the lens. If sunlight can reflect off the back of the lens and into your eye you need an AR Coating. Sunglasses that claim to filter out 100% of UV rays will actually provide no protection at all if sunlight is reflecting off the backside of the lens directly into your eye.
Some of the newest AR coatings have also been better engineered to increase the scratch resistance of the lens.
The term "AR coating" is actually a bit misleading. It takes several metal oxide coatings to create the optical interference that counteracts reflected light waves and allows more light to be transmitted through the lens. Each layer is scientifically engineered to work with a specific segment of the color spectrum. So far, no one has figured out how to do this across the entire color spectrum without adding a slight tint to the lens. On clear dress eyewear, this might be a slight yellowish-green or purple cast. If the coating is on the front of the lens, your eyes will be more visible because the lens is less perceptible. AR coatings on sunglasses are just as effective, but less noticeable.
If you buy a Clear lens or a Transitions lens you should consider an AR Coating. This will reduce the ”starburst” effect caused by light bulbs or headlights, and it will allow a Transitions lens to darken a little more, and a little faster.
When you clean a lens that has an AR coating, USE A CLEANER THAT IS APPROVED FOR AR LENSES. Many cleaners designed for regular glasses will wreck an AR coating. (See Accessories for AR-Safe lens cleaner.)
ADS Eyewear is an optical company, not just a sunglass distributor. ALL of the glasses on this site are selected to improve your vision and preserve your sight. If an AR coating should be applied, it is. And when you receive an AR coating from us, it will be good one.
All glasses from Maui Jim and Kaenon have an AR coating on the back of the lens, as does the Bolle Metals Collection.
Flash or Mirror Coatings:
A flash coating, also called mirror coating, is the opposite of an AR coating. Flash coatings reduce glare by reflecting it off the front of the lens before it can be amplified between the lens surfaces. The mirrored appearance will also prevent other people from seeing your eyes.
The color of a flash coating is only visible from the outside. If a gold flash is put on a blue lens, it will appear blue to the person wearing it, and gold mirror to everyone else. The color of the flash coat does not affect how color is perceived. It only acts as a shield against glare.
Photochromic Lenses:
Photochromic lenses change from a light to a dark tint based on the amount of sunlight or UV exposure. Silver halide is mixed with the lens material to cause this transformation. Photochromic lenses are very versatile and very popular with motorcyclists who want to carry only one pair of glasses. Bikers with a helmet shield should confirm that it does not block the UV rays required to darken their photochromic glasses.
Important Note About Photochromic Lenses:
We use Transitions brand photochromic lenses, and we consistently use only the most recent version of this product. So it is not possible to get a better transitions lens than the lenses that we offer. BUT, there are a few important facts that you should know before purchasing them.
- Transitions material will not get quite as dark in polycarbonate or Trivex lenses as it will in glass or CR-39 (plastic).
- Heat will slow down the darkening process in Transition lenses.
- After 3 -5 years, Transitions lenses will start to “Fatigue”. This means that after a while they will not get quite dark or as clear. Keeping the lenses out of extreme temperatures (like on the dash of your car) will extend the life of Photochromic lenses.
Motorcyclists and bicyclists often request photochromic lenses so they won't have to change their glasses or lenses when the sun sets. Glass or CR-39 lenses are not strong enough for sports eyewear, so polycarbonate or Trivex are your only options. If you want these lenses to be completely clear at night, they will only get about 60% to 75% as dark as traditional dark glasses during full sunlight. Some people choose to have a slight tint added to their photochromic lenses to compensate for this condition. Copper is a good choice because it adds contrast in low light conditions.
Cheap Sunglasses: Are They Worth It?
We hear it all the time: "Why should I pay more for your sunglasses when I can buy them at Exxon or Wal-Mart for 20 bucks?"
The reason you would pay more has nothing to do with making a fashion statement or wearing a recognizable brand name. Sunglasses are worth more if they help you see better, play better, or react faster. Here are a few things to look for:
Lens Consistency:
Most sports lenses are made of polycarbonate. It is virtually unbreakable, it naturally blocks UV rays without additional coatings, and it is optically a great product. But not all polycarbonate lenses are created equal. A quality lens is manufactured to the same precision standards whether it is a prescription lens or not. Many of the Nike lenses in their big-wrap frames are even ground with a slight negative prescription to compensate for the curvature of the lens. (This is called “Decentering” the lens.)
Even more important is the consistency of the material used to produce a lens. When polycarbonate is heated to a liquid form the most dense material settles to the bottom. Light passing through a lenses made from this dense, pure polycarbonate will travel in a straight line. This produces the truest, clearest vision. Lenses that are made from the more porous, less pure material that rises to the top in this process will have inferior optics. This material is found in the less expensive sunglasses sold by discount stores. The markup on those glasses is much higher than you will find on quality eyewear.
It costs much more to make optically superior lenses. You may not recognize the difference in these lenses while you’re in the store, but you will see a major difference when you try to judge the flight of a ball or go over an uneven surface.
Look-Alikes:
If it looks too good to be true, it is. Bolle and Serengeti are excellent examples. These are both manufactured by Bushnell Corp. Bushnell is well known for quality camera lenses, binoculars and telescopes. But when they had an opportunity to sell huge amounts of eyewear to Wal-Mart they used foreign manufacturers to produce cheaper versions of their best-known models. These cheaper glasses are almost identical to the models that we sell, but the lenses are much thinner and clearly inferior. If you have a Wal-Mart version of Bolle glasses and you order replacement lenses from us, they will not fit. Our Bolle replacement lenses are too thick to fit in Wal-Mart's Bolle frames. (The Wal-Mart version of Bolle glasses are sold on several web sites, but NOT on ours.)
Scratch Resistance:
Conventional wisdom would lead you to believe the scratch resistance is a fundamental measure of lens quality. You may be surprised to find out that many of the cheapest lenses can have better scratch resistance than more expensive lenses. This is because the hardeners applied to the lens surface have a different index of refraction than the lens material. This causes light to pass through the lens at a different speed than it passes through the coating. The result is blurred vision. A quality lens has a perfectly uniform scratch coating that is engineered not alter the path of light passing through the lens. These quality coatings may not be slathered on as thick as the cheaper coatings, but your vision will have less distortion and more contrast with a properly applied scratch coating. That’s why a quality eyewear case is a great investment.
UV Protection:
Protection from the sun’s Ultra Violet rays is one of the most fundamental reasons we wear sunglasses. Promoting sunglasses with a headline that reads “Blocks UV Rays” is the equivalent of advertising tires that “Hold Compressed Air!”
Every pair of sports eyewear we sell provides maximum UV protection, but you may not find this fact posted all over our web site. We consider this a basic responsibility, not a promotional gimmick. Even our clear sports lenses block UV rays.
In summary, cheap glasses typically do not deliver the visual clarity required for sports activities. When you see better you have faster reflexes and make better decisions. Cheap sunglasses are great for ZZ Top concerts or lounging around by the pool. The eyewear on this site is for people who rely on clear vision to enjoy their time in the sun.