One-way mirror. American police uncle likes this very much! In this way, the other party does not see the eyes and expressions of the police, which is conducive to self-protection.
The color of the specular reflective coating is varied, depending on the thickness and structure of the coating, while the wearer's visual perception is not colorful, usually brown or gray. Reflective coatings reduce the light passing through the lens by 10-60%, making them ideal for deserts, seas, rivers, snowy mountains and high altitudes. It is very popular in extreme sports.