The microscopic photochromic particles embedded in the lens of the Tifosi Lore Sunglasses - Gloss Gunmetal All Terrain Fototec react to light rays so they darken when the sun is bright and lighten when the sun goes down. The result of this cycling technology advancement is that one pair of sunglasses with one set of lenses is all you need. The light transmission rates of the Fototec™ lenses range from 38.2% to 12.2%. Besides providing 100% protection against harmful UVA/UVB rays, the Fototec lenses prevent glare from straining your eyes. Adding to the clarity is the optically decentered design that eliminates distortion. Lightweight, and with a smooth surface for air to flow over, the lens is also scratch resistant and shatterproof so the glasses are exceptionally durable. The lenses are also vented so air flows over them and there is never any fogging. The frame is made of Grilamid TR-90 that has a high resistance to chemical and UV damage as well as enough flexion so it won’t break.