These are lenses that darken as you go from indoors to outdoors. They are available in both glass and lightweight hard resin. They darken to a moderate shade of grey. Ask for a demonstration of photosensitive lenses. Polycarbonate Polycarbonate lenses are the most impact resistant lenses available and are always the lens of choice for young people and active patients.
Polycarbonate lenses are high index and are usually the lightest, most comfortable lenses.
They absorb all harmful UV light and can be made with ultra thin edges because of their unique strength. For years glass was the only lens material available and glass still offers superior optics. The most scratch-resistant material, the primary disadvantage of glass is its weight, generally twice that of hard resin. Glass lenses are heat or chemically treated to increase impact resistance.