Mirrored sunglasses with lenses that reflect light like mirrors. The lenses feature a thin reflective coating — because the coating is so thin, it is called a semi-silvered surface. The term “semi-silvered” comes from the fact that the reflective molecules on the lens are very sparse, about half the number that would make the lens opaque. At the molecular level, reflecting molecules are evenly dispersed across the surface of the lens, forming a uniform film that covers only half of the lens. This silver-plated side reflects about half of the light that reaches it while letting the other half pass through directly.
Typically, mirror coatings are gradient, with the color depth of the paint gradually changing from top to bottom. That will enhance the sunglasses’ ability to resist light from above. At the same time, it allows more light to enter from below and horizontally. That means sunglasses can block out the sun’s rays while also allowing you to see the dashboard when you are driving. Sometimes, paint is double gradual. The depth of color is highest at the top and bottom of the lens, while the middle of the lens is clear.
The critical problem with mirrored sunglasses is that the paint can easily scratch. Sunglass manufacturers have not yet succeeded in coating reflective film with a scratch-resistant coating. Thus, the scratch-resistant layer is coated on the surface of the lens, and the reflective film is coated on top of the scratch-resistant layer. So if you buy mirrored sunglasses, take care to avoid scratching the surface of the lenses!