Lens Materials: CR-39 Plastic, Polycarbonate, High Index, Trivex, Glass
Lens Treatments: Polarization, Anti-Reflective Coatings, Mirror Coatings, Photochromics
CR-39 is the most frequently used lens material in prescription eyewear. It is generally the least expensive, and it works fine in almost all environments. CR-39 lenses are excellent for eyeryday tasks, provide very clear vision, and are significantly lighter than glass lenses. However, if you are an active participant in any sporting or “safety” activities, you need a quality polycarbonate or Trivex lens in front of your eyes.
Polycarbonate is virtually unbreakable, and it is used exclusively by many of the world's finest drill mount and sports glasses manufacturers. It is thinner, lighter, and stronger than plastic and glass. It is well suited for children’s eyewear, safety eyewear, “wrap” sunglasses,
Polycarbonate naturally blocks almost all of the sun's harmful UV rays, so no coatings are required to block UV rays on a polycarbonate lens. 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 more easily scratched. New lens coatings and hardeners have significantly improved polycarbonate's durability, but choosing a polycarbonate lens still requires an informed consumer.
High Index 1.56, 1.60, 1.67, and 1.74
“High Index” lenses encompass the entire range of thinner, lighter optical materials (thinner and lighter than CR-39 plastic and Glass). These are wonderful, all purpose lenses like CR-39, yet they will always make a more attractive and more comfortable pair of eyeglasses.
The term “high index” refers to a high index of refraction (bends the light at a greater rate). So, if the light is bent at a greater rate through a lens, you don’t need as much material, and the curves can be made more shallow - that is what creates a thinner and lighter lens.
Many high index lenses are made with additives that make the lenses work extremely well for drill mount rimless frames. Empire Optical uses High Index lenses with MR-10 additive that make all of our high index products as resilient as possible.
Trivex is a new lens material that is quickly becoming the best thing that has ever happened to drill mount and sports eyewear. Originally developed for military applications, Trivex is stronger, clearer, and lighter than 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. We believe in Trivex so much, that we offer a full 2 year replacement guarantee if you can manage to crack or break them.
Trivex naturally blocks 100% of the sun's harmful UV rays, similar to polycarbonate. Trivex has better scratch resistance than polycarbonate.
Glass lenses provide excellent scratch resistance and clarity. They are also about twice as heavy as other materials. Although glass lenses must be chemically hardened after production, they are indeed the “most dangerous” lenses you can wear in front of your eyes. Once a glass lens becomes scratched (or scored) it creates a fault on that hardened surface. Any subsequent impact on that fault can cause the lens to shatter into very dangerous slivers. We can certainly produce glass lenses, but will try to advise against it unless it is the only option for your specific eyewear needs.
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 reflected glare (which is light dispersed in many directions) is blocked allowing you to see more comfortably, and with less eye strain. 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.
Anti-Reflective (AR) Coatings
Typically, about 8% of the light that hits a lens is reflected off. AR coatings allow almost all of that light to pass through to your eye. People generally consider Anti-Reflective coatings for cosmetic reasons because they make your lenses look like they “disappear.” However, a good AR coating can also help your eyes relax in a fluorescent work environment, and help with night driving by reducing the ”starburst” effect caused by headlights. Most high quality AR coatings also have superb warranties for scratch replacement, which means your “investment” in good lenses will keep you protected for a couple of years.
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.
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 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 customers who want to carry only one pair of glasses for clear and sun. The main brand name you hear mentioned is “Transitions ® Lenses” and Empire Optical uses the latest technologies to ensure the highest performance.
There are several different types of Transitions Lenses for different uses including lenses that return to completely clear, a darker lens that always keeps a residual tint (for those who are light sensitive), and a sunglass lens that goes from a medium to a dark sunglass depending on the UV conditions outside. Come in to Empire and we will let you look through the samples of each style of Transitions Lenses before you choose.
® Transitions is a registered trademark of Transitions Optical, Inc.