Quality glass lenses offer the best viewing quality and the most scratch-resistant. Two of the most prestigious and famous sunglasses brands make glass lenses their distinctive trait: Ray Ban and Persol. However, glass lenses will be heavier, cost more money and are more prone to shatter when hit, so could not be the right choice for every situation.
Plastic, Organic plastic, CR-39
CR-39, or organic plastic (and similar compounds) is thinner and weighs half as much as glass, and it is the widest used material for general purposes sunglasses today. It exceeds the FDA requirements for impact-resistance, but it is not shatter-proof, so it is not recommended for active sports.
A remarkable strong plastic, it weighs the least and is the most impact-resistant (it can resist to the impact of a steel ball travelling at 160km/hr!) making it a perfect choice for rugged sunglasses. They also offer built-in ultraviolet filtering. These are a good choice for kids sunglasses, sports and outdoor activities, and safety glasses.
Nylon, or polyamide, is a newer top-notch performance material, it combines the advantages of polycarbonate and CR-39 lenses. Nylon lenses have an outstanding shock resistance while being extremely lightweight, and to do not crack when drilled (making them perfect for some frame shapes). Increasingly used in general purposes eyewear, and for active sports.
For years, polarized sunglasses have been used by boaters and fisherman to reduce glare from the water that they spend so much time on. In the past few years, however, the benefits of polarized sunglasses have been realized by a variety of other outdoor sports enthusiasts as well as by drivers and general use wearers as well. Thus, the popularity of polarized sunglasses has increased dramatically, as their availability.
The activities that utilize the benefits of polarized sunglasses the most include, other than water sports, skiing, golfing, biking, and jogging. For these activities they offer a clearer view and eliminate glare.
How Do Polarized Lenses Work?
Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses. The result: a reduction in annoying and sometimes dangerous glare.
The bottom line is that whether you spend your time boating or waterskiing, skating or mountain biking, driving or jogging, polarized sunglasses are an excellent choice for sunwear.
However, some people find polarized sunglasses annoying because the polarization filtering makes some LCD screens unreadable (as also monitors are often polarized to increase the sharpness and contrast), and some car's displays as well.
What are photochromic lenses? A photochromic lens is the type of lens that changes its color/tint depending on the amount of light (ultraviolet rays) that are cast upon the lens. When more light is encountered, the lens becomes darker. Conversely, when less light is shined then the lens becomes lighter in color.
How do photochromic sunglasses work?
The secret is in the active material that gets mixed into the lens material. The material is called Silver Halide and it is mixed evenly within each lens. The Silver Halide is the material that makes the lens change its color based on ultraviolet ray exposure. Most photochromic lenses were originally made out of glass mixed with Silver Halide but recently some lenses are now made out of plastic or even polycarbonate materials.
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 color, depending on the individual manufacturers process. Each layer is calculated to block reflected light resulting in a reduction in glare, annoying reflections and halos around light sources. AR coatings are most useful on water and snow.
Mirror or Flash
Highly reflective and greatly reduces the amount of light that reaches your eyes. Generally applied over a dark sunglasses lens, but can be applied over any base color. Mirror coated lenses absorb anywhere from 10% to 60% more light than uncoated lenses. These are good for higher altitudes, sand, water and snow. Although the most common are the silver, gold and copper metallic coatings, you will find many colors available nowadays.
No lens material is scratch-proof, although a lens that is treated front and back with a clear, hard coating does become more resistant to scratches. Most types of plastic lenses have built-in scratch-resistant coatings.