What are mirrored lenses?
Highly reflective coating greatly reduces the amount of light that reaches your eyes. Mirror coated lenses absorb anywhere from 10% to 60% more light than uncoated lenses.

How do mirrored sunglasses work?
Generally applied over a dark sunglasses lens, but can be applied over any base color as well as polarized or non-polarized lenses.

These are good for higher altitudes, sand, water and snow. Although the most common are the silver, gold and copper metallic coatings.