Photochromic Lenses: How Do They Work?

Same lenses. Same frames. They’re clear indoors. They darken into sunglasses outdoors on a sunny day. No fumbling around to find your sunglasses when you step outside.  Photochromic lenses perform an amazing dual function of being clear indoors and darkening into sunglasses outside. But how do they work? 

First, let’s understand the funny name, “photochromic,” which comes from two Greek words, “photos” meaning light and “chroma” meaning color. In other words, the name literally means color changing in response to light. In a nutshell, that is essentially what happens with these special lenses.

Photochromic technology has been around since the early 1960’s and was inspired by the same method used to develop photographic film.  Camera film is embedded into glasses with tiny silver crystals that turn opaque and darken when exposed to light. Similarly, the first photochromic lenses were made of glass embedded with microscopic silver crystals that reacted to light by turning opaque and darkening. This reaction to light caused the lenses to darken. The reaction, however, was reversible. When the lens moved out of the light (indoors, for example), the silver crystals changed their structure and became less opaque which resulted in the lens turning transparent and clear.

Today’s lenses typically use an extremely thin coating of organic (carbon-based) molecules called naphthompyrans to achieve the same result, only faster. Today’s photochromic lenses are activated by exposure to UV light, abundant in the form of sunlight, which is perfect for turning clear lenses into sunglass lenses when you move outdoors into the sun.  Artificial light does not contain UV rays (and modern windows block harmful UV rays from entering indoors), therefore, reliance upon UV light to activate the change in color of the lenses helps to explain why photochromic lenses remain clear indoors under artificial light.

Recently, technology has been developed that aligns the photochromic molecules uniformly parallel and in such a way that they behave like a polarized filter. As a result, we now have polarized photochromic lenses that - when turned dark - the lenses act like standard polarized lenses that block irritating glare, enhance color saturation, and deliver a very comfortable view in bright and glary environments.

There is no need to buy multiple pairs of prescription glasses when you can choose a hybrid lens that does it all in one.  Photochromic or polarized photochromic lenses are a fantastic solution for anyone seeking convenience and comfort in any environment.