Bifocal reading glasses: accommodate for both near and far vision by adding a unique lower lens with add vision value for reading and near vision. Transition photochromic gray bifocal reading glasses 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.