Photochromic lens in mass contains silver halide (silver chloride, silver bromide) microcrystals. When exposed to ultraviolet or short wave visible light and other activated light, halogen ions emit electrons, which are captured by silver ions. The following reactions occur: colorless silver halide decomposes into opaque silver atoms and transparent halogen atoms, and silver atoms absorb light to reduce the transmittance of the lens. Since the halogen in the color changing lens will not escape, a reversible reaction can occur.

After the active light is removed, the silver in photochromic lens in mass is combined with halogen to make the lens return to the original transparent colorless or light tone state. The content of silver halide microcrystalline particles in the color changing lens is about 4 × 1015 pieces / cm3, the diameter is about 80-150 μ m. The average distance between particles is about 600 μ m。 To is the original transmittance of the color changing lens before exposure, TD is the original transmittance of the color changing lens at 5 × The transmittance at 550nm was improved after 15 minutes of exposure to 104lx xenon lamp; THF is the half recovery time, that is, the time required for the transmittance of the color changing lens to return to normal after stopping exposure.

High quality photochromic lens in mass should be transparent, free of emulsion color, short half recovery time and fast recovery. The original transmittance of the color changing lens without primary color is about 90%. The original transmittance of the primary color changing lens can be as low as 60-70%. The transmittance of general sunglasses is reduced to 20-30% after light discoloration. The color change of comfortable lens is shallow, and the transmittance is about 40-50% after light change.

The glass containing silver bromide (or silver chloride) and trace copper oxide is a kind of color changing glass. When exposed to sunlight or ultraviolet light, the silver bromide in the glass decomposes and produces silver atoms (AgBr = = Ag + BR). Silver atoms can attract visible light. When silver atoms gather to a certain amount, most of the light emitted on the photochromic lens in mass is absorbed, The original colorless and transparent glass will turn gray black at this time. When the discolored glass is put in a dark place, under the catalysis of copper oxide, silver atoms and bromine atoms will combine to form silver bromide (Ag + br = = AgBr). Because silver ions do not absorb visible light, the glass will become colorless and transparent again. This is the basic principle of photochromic lens in mass glass discoloration.