Should I purchase a sunglasses with a glass lens?
Well, here are some facts about glass lenses that might help you reach a better decision.Glass is the only lens material that can be made into 100% optically correct sunglasses. For true vision, there is no comparison between glass and other lens materials.
Glass does not flex or compress. Whenever lenses are placed into an eyewear frame, they are held in place by pressure of some kind. Plastic lenses flex and that creates distortion; but that cannot happen with glass lenses.
Glass does not expand or contract in heat and cold in a significant way. No matter what the temperature outside, 100% optically correct sunglasses will remain 100% optically correct.
Glass is the hardest material, and the most scratch-resistant. Glass is the most durable, and longest-lasting sunglass lens material. However, it is not scratch proof. Sand can scratch glass, but it requires serious effort or trauma to scratch glass lenses.
Technology has made it possible to create a very lightweight glass lens. Today, it can be difficult to tell the difference between glass and plastic, even when holding a pair with glass lenses in one hand and a pair with plastic in the other hand. (Of course, the difference is clear when looking through the lenses. But the weight of the lens is no longer a dead giveaway as to which is which.)
The danger of shattering was once one of the major disadvantages of glass lenses. However, all glass lenses pass the "Drop Ball Test" for impact resistance - the same test that is administered to polycarbonate and CR-39 lenses. When today's polarized lenses tend to break in a similar pattern as a car windshield. The broken pieces of glass mostly stick to the polarizing film that is inside the lens.
These Spotters had been stepped on by the customer. Notice that the broken lens has retained its original curvature. The broken lens pieces were still so tightly held by the frame that we had to smash the broken lens out of the frame with a hammer (it took more than a few smacks, too!). This isn't to say in any way that glass lenses are equivalent to safety glasses. However, polarized glass lenses are much, much less likely to cause injuries today than they ever have been in the past.