- C$59 for C$200 worth of prescription eyeglasses or sunglasses
Transitional Lenses: Instant Shade for Your Eyes
Doing away with the burden of swapping prescription glasses for a blindfold every time the sun comes out, transitional lenses—more accurately known as photochromic lenses—almost seem like magic. Indoors, the lenses are clear, but outside, they darken as if transforming into a separate pair of sunglasses, shading your eyes from seeing the sun in its bathrobe.
The keys to the transition are the UV rays of natural light. In glass lenses, the glass is embedded with crystals of silver chloride or silver halide. When exposed to UV rays, the crystals combine with the glass molecules, forming elemental silver, which appears dark compared to the clear glass. These days, however, most photochromic lenses are made of plastic. Instead of silver molecules, the lenses use an organic dye. UV rays break the chemical bonds, causing the molecules to rearrange into a form that absorbs the visible wavelengths of sunlight.
- The Corning Glass Company—notable today for producing the durable glass on smartphones—invented the first photochromic lenses in 1960.
- Many photochromic lenses don’t work while driving, since car windows filter out UV light. Ask your optician about alternative transitional-lens options that do work inside vehicles or spaceships headed toward the sun.