Different Lens Materials
I want to address sunglass lens materials, as there is lot of misinformation regarding this topic. After reading this blog you will have a better understanding enabling you to make a more informed decision when purchasing sunglasses.
GLASS: Glass lenses have been around forever. Glass is considered to produce the best optics of all lens materials. These lenses are the heaviest and least impact resistant of all the lens materials. In the early 1970’s the FDA made a ruling that all glass lenses had to be treated to resist impact. This treatment can be accomplished by several techniques, all of which involve heating the lens. The FDA made polarized glass lenses exempt from the ruling as the heating process melts the polarizing film. Glass material is not an ultraviolet screen and has to be treated to filter these wavelengths and only a few lens tints are available.
HARD RESIN: This lens material is also called CR39 and is available in a variety of refractive indices. The higher the refractive index the lighter the weight of the lens. CR39 scratches easier than glass so most sunglasses with CR39 lenses have a scratch resistant coating applied to the front and back surfaces. CR39, other than in high index, does not filter ultraviolet and must be treated to do so. CR39 can be manufactured in a wide variety of lens tints. CR39 has excellent optical properties and is the most widely used lens material by eye care professionals in the USA.
POLYCARBONATE: Polycarbonate is the optical name for Lexan, or “bullet proof glass”. This lens material is lighter in weight than CR39 and about 15% the weight of glass. Polycarbonate is the most impact resistant lens material in the sunglass market. Optics have improved to a high level since the material was introduced many years ago. Polycarbonate is the “go to material” for high impact resistance. Tint and polarized tint options are nearly unlimited and the material is an ultraviolet screen without any special dyes or coating. Lenses fog less and clear faster than any other lens material.
TRIVEX: This material is the new entry into the sunglass lens lineup. Impact resistance rivals that of polycarbonate. Lenses are light in weight with excellent optical properties. Polarized tint options are somewhat limited. This material is the most expensive of the four major lens materials.
I hope that this information will help you make an informed intelligent decision when purchasing your next pair of sunglasses.