The lenses of the color-changing glasses can be darkened after the sun's rays are emitted. When the lighting fades, it becomes bright again. This is because the crystal of silver halide is working. Under normal conditions, it keeps the lens perfectly transparent. Under the illumination of sunlight, the silver in the crystal separates, and the free silver forms a small aggregate inside the lens. These small silver aggregates are irregular blocks that are interlaced by dogs. They are unable to transmit light, but only absorb light, which results in darkening of the lens. In the case of light darkness, the crystals are re-formed and the lens returns to a bright state.