SPORTS VISION BLOG SERIES PART 2
Written by: Leesa Nesty
This week we are excited to present Part 2 in our blog series by Doctor Gary Nesty, Solar Bat owner. There are so many important factors to consider when purchasing the correct pair of sunglasses for your self and your chosen sport. Dr. Nesty is an expert in his field and we are happy he is sharing his expertise with us and helping us make informed decisions. Stay tuned for future posts from Dr. Nesty sharing with us about how improved performance in our chosen sports can be determined by proper lens tints. Please enjoy this and the future posts from Dr. Gary Nesty.
SPORTS VISION PART 2
by: Dr. Gary Nesty
I want to address lens materials in this the second of a series of blogs aimed at visual performance in your chosen sport. There is lot of misinformation regarding lens material and hopefully 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 have 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 but all involve heating the lens. The FDA made polarized glass lenses exempt from the ruling as the heating process melts the polarizing film. Glass lens blanks are not available in large sizes thus the size of the lens in a sunglass is limited. Glass material is not an ultraviolet screen and has to be treated to filter these wavelengths.
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 lens blanks are available in large sizes so sunglass frames can have larger lens sizes. 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 in polycarbonate lenses have been perfected since the material was initially introduced. Polycarbonate is the “go to material” for high impact resistance. Polycarbonate lens blank sizes will accommodate large eye size sunglass frames and still be very light in weight. 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 is a new entry into the sunglass lens material 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.
Posted by Gary Nesty on July 12, 2013 in Solar Bat® Blog.