Production principlePolarized sunglasses block unpleasant glare and protect your eyes from UV rays. All of this is due to the metal powder filter, which "selects" the light as it enters. Polarized sunglasses selectively absorb some of the wavelength bands that make up the sun's rays because they rely on very fine metal powders (iron, copper, nickel, etc.). In fact, when light hits the lens, the light is diminished based on the so-called "destructive interference" process. That is to say, when light of certain wavelengths (herein referred to as ultraviolet light a, ultraviolet light b, and sometimes infrared light) passes through the lens, they cancel each other in the direction of the inner side of the lens, that is, toward the eye. The mutual overlap of the formed light waves is not an accidental phenomenon: the peaks of one wave are combined with the waves of the waves that are close to them, resulting in mutual cancellation. The destructive interference phenomenon depends on the refractive index of the lens (ie, the extent to which light deviates from the air through different materials) and also depends on the thickness of the lens. In general, the thickness of the lens does not change much, and the refractive index of the lens varies depending on the chemical composition.
Finally, the lenses of polarized sunglasses can darken after the sun's rays are shining. When the lighting fades, it becomes bright again. This is because the crystal of silver halide is working. Under normal conditions, it maintains perfect transparency of the lens. 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 in the form of irregular blocks that are interlaced by dogs. They are incapable of transmitting light and only absorb light, which results in darkening of the lens. In the case of light, the crystals are re-formed and the lens returns to a bright state.