A common problem with sunglasses is called back-glare. This is light that hits the back of the lenses and bounces into the eyes. The purpose of an anti-reflective (AR) coating is to reduce these reflections. It consist of several layers of metal oxides applied to the front and back lens surface. Because of the layering effect, AR coatings sometimes have a hint of green or purple colour, depending on the individual manufacturers process. Each layer is calculated to block reflected light resulting in a reduction in glare, annoying reflections, this is a great safety benefit when you’re driving at night. These coatings are particularly effective for reducing eye fatigue for computer operators and anyone driving at night. And, of course, with ordinary glasses, headlight from cars can be an pain, the Headlight glare can be a real problem, Headlight glare is diminished with anti-reflective coating applied to lenses. Each layer is scientifically calculated to block reflected light.
Most eyeglass lense material, not even glass has scratch-proof resistant. However, a lense that is treated front and back with a clear, hard coating does become more resistant to scratching. Nowadays, most types of plastic lenses, including high-index, polycarbonate and traditional plastic materials, have built-in scratch-resistant coatings. Since it is sometimes optional, make sure your optician knows that you want scratch-resistant lenses in your prescription eyeglasses.
Another type of lense treatment that is beneficial (invisible to the naked eye) is ultraviolet (UV) protection. Just as we use sunscreen to keep the sun’s UV rays from harming our skin, UV treatment in eyeglass lenses blocks the same rays from damaging our eyes. Over-exposure to ultraviolet light is thought to be a cause of cataracts, retinal damage and other eye problems. An ultra-violet treatment is simple and quick to apply to most plastic eyeglass lenses, and it does not change the appearance of the lenses at all.
In contrast to anti-reflective coatings, which are very clear, mirror coatings (also called flash coatings) are bold statements of color. A mirror coating is highly reflective. The mirrored sunglasses associated with state troopers are one example of a flash coating. The technology has advanced, however, so that today’s choices include colors of silver, gold and copper metallic mirror coatings, even Hot pink, blue almost any color. Mirror coatings are purely cosmetic: the wearer perceives no difference in vision regardless of what color the coating is. Only those looking at the person wearing the glasses can see the color of the mirror coating. Mirror coatings are generally applied over sunglass-dark lenses. Obviously, a highly reflective flash coating prevents others from seeing the eyes of the wearer. Well with mirrored lenses they have a reflective effect to give a mirrored look the lenses have a very thin reflective coating, which is sometimes called half-silvered surface, the half-silvered surface will reflect half of the light that strikes its surface, while letting the other half go past straight through. The mirrored lenses can absorb anywhere from 10% to 60% more light than uncoated lenses and additional protection from light straight ahead, they are good for altitudes, sand, water and snow, to help with high reflections and reduces a large amount of light that reaches your eyes. With mirrored lenses the main problem is that the coatings are easily scratched, this is because as the manufacturers have not been able to successfully apply a scratch-resistant layer on top of the reflective coating, the only way it can be done at the moment is by applying the scratch-resistant coating first to protect the lenses then the reflective coating.