1. What are photochromic lenses? Photochromic lenses are also referred to as light-sensitive lenses". Glass lenses are adding silver halide, but now is the mainstream of photochromic resin lenses, adding of spiro and other chemicals in the acrylic resin lens, so that the original colorless and transparent lenses. in bright light, will become colored lenses, to do the protection, so is suitable for indoor and outdoor use. Photochromic lens optical glass containing silver halide microcrystals, phototropy reversible reaction according to the principle, in the sunlight and UV irradiation variable dark, completely absorb ultraviolet and visible light absorption of neutral; back to the dark, can restore the colorless transparent. Photochromic lenses are mainly used in open-air fields, snow fields and indoor light sources, so as to prevent sunlight and ultraviolet light from damaging the eyes. Butterfly reading glasses is a perfect bifocal glasses for women/men. The reading lens contain two ares which are reading area and distance area. The reading part help to magnify tiny words so that the wearers can read more easy. The distance area help wearer see things from long distance. 2. Test discoloration? it is recommended to test at noon, noon sun UV strong, discoloration can achieve the best results, more test several times, the effect is better. Warm tips Please correctly understand photochromic glasses, he color depth does not equal sunglasses.