On some lenses, the mirror coating decreases the amount of light passing through the lens by a whopping 60%. The mirrored lens protects the eyes from glare by reflecting the glare. This isn’t to say that the mirroring is useless. The lens itself needs to be tinted to provide a high degree of UV-protection – just using the metallic coating is not enough. Mirrored lensesĪ mirrored lens has a metallic and partially reflective coating on the outer side of the lens. The most common configuration for gradient lenses is to be really dark at the top and then gradually become lighter until it is almost or completely clear at the bottom. Gradient lenses aren’t uniformly colored. It has a lot of desirable qualities, but is also expensive compared to most other alternatives. The above mentioned SR-91 is a non-polycarbonate material introduced by the luxury performance eyewear brand Kaenon in 2001. The first CR-39 eyeglass lens was created in 1947 when the war was over.
Another low-weight alternative is CR-39, a plastic polymer originally used to produce reinforced plastic fuel tanks for the B-17 bomber aircraft. Polycarbonate plastic lenses are famous for their low weight and for being almost shatterproof. A major downside is that glass weighs more and can shatter on impact. Glass lenses tend to have better optical clarity than plastic lenses, and also be more resilient to scratches. Low-priced sunglasses usually have plastic lenses, while more expensive ones can have plastic lenses, glass lenses or lenses made from proprietary materials such as SR-91. A majority of the sunglasses sold worldwide are non-corrective (plano) glasses, but it is also possible to have sunglasses made according to your eyeglass prescription. Sunglasses can be used to prevent bright sunlight from discomforting and injuring the eyes.
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