Photochromic Lenses (what we call "Indoor / Outdoor lenses"): How Do They Work?

Same lenses. Same frames. They’re clear indoors. They darken into polarized sunglasses outdoors on a sunny day. No fumbling around to find your sunglasses when you step outside.  Indoor / Outdoor lenses - also known as Photochromic lenses - perform an amazing dual function of being clear indoors and darkening into polarized 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.

Curious if photochromic lenses block blue light from your screens such as your computer screen, tablet or phone?  The answer is: YES.  Anti-blue light filters are built into the photochromic lens itself so these lenses will provide protection from blue light while you are working on your computer or other screens.  And - yes - Indoor / Outdoor lenses also block harmful UV rays.

L&F uses the latest generation polarized photochromic lenses that turn darker faster (and turn clear faster, too!).  And when turned dark, the lenses become polarized lenses that block irritating glare, enhance color saturation, and deliver a very comfortable view in bright and glary environments.  

Have a question about the light-changing photochromic lenses?  Click this link to send us a question. We're quick to respond and we're happy to help in any way we can.

There is no need to buy multiple pairs of prescription eyeglasses and Rx sunglasses when you can choose a hybrid lens that does it all in one.  L&F Indoor / Outdoor Lenses (polarized photochromic lenses) are a fantastic solution for anyone seeking convenience and comfort in any environment.