Lens Material

For Eyeglasses and Sunglasses

Plastic(Hard Resin)(CR-39):

Standard plastic lenses can be easily tinted to almost any color. They are half the weight of glass. Although CR-39 can scratch easier than glass, it can be treated with a scratch resistent coating. Hard resin lenses are more impact resistent than glass, making them safer.

Hi-Index (Thinner and Lighter Lenses):

The higher the index of refraction of a material, the thinner the lens can be and still bend the light the same as a conventional material. This allows for a much more appealing looking pair of glasses, especially in higher prescriptions. Since less lens material is needed in high index, it is much lighter. The high index material itself, blocks nearly 100% of harmful UV light and is tintable.

Polycarbonate:

Lenses made of polycarbonate material are the most impact resistent in the world. They are always the best choice for sports glasses, active children, and for protecting patients with only one usable eye. Polycarbonate blocks UV light. It is an entry-level type of hi-index material, so lenses are thinner and lighter than standard plastic.

Photochromic (Lenses That Darken In The Sun):

These lenses are available in glass (Photogray), plastic (Transitions), or polycarbonate (Transitions). They are activated by the UV spectrum of direct sunlight and protect the eyes from these damaging rays. Photochromics were originally designed to give a moderate tint outdoors, but now there are tints that change to a true sunglass (Transitions Extra Active in plastic and Photosun in glass). Since most windshields have good UV blockage, photochromics don't work well inside the cab of vehicle.

Glass

Glass was the only option one had in optical lenses for many years. It offers excellent optics and superior scratch resistence, but is double the weight of plastic. It must be heat or chemically tempered to increase its impact resistence. Even then, it still does not come close to matching the other materials for shattering prevention.