The Science of Shade: Unlocking Photochromic Lenses

By: Austin Henderson  | 
A business man driving his car.
Photochromic glasses refer to a specific chemical reaction lenses have to bright light and ultraviolet (UV) radiation. Zorica Nastasic / Getty Images

You've seen it happen—a friend walks inside and their prescription sunglasses magically transform into clear eyeglasses. No, it's not an optical illusion; it's optical science!

Photochromic lenses are eyeglasses that auto-adjust from clear to tinted. But how do these modern marvels shift shades so effortlessly? Let's delve into the light-manipulating alchemy behind photochromic technology.


Tracing the Transition: A Brief History of Photochromic Lenses

The timeline of photochromic lenses begins with Corning Incorporated, a U.S.-based material science company known for innovations in glass, ceramics, and other advanced technologies.

They were the pioneers in developing the first-ever glass photochromic lenses back in the late 1960s. This groundbreaking invention laid the foundation for the photochromic technology we know today.


Fast forward a few decades, and the term "transition lenses" burst onto the scene, popularized by Transitions Optical in the 1990s. Now, we enjoy a variety of options — from the original glass lenses to modern plastic photochromic lenses, and even progressive lenses that employ this optical science.

The Chemistry of How Photochromic Lenses Work

Embedded in your photochromic lenses are molecules of silver compounds, such as silver halide and silver chloride. When you wear photochromic lenses indoors away from sunlight, these molecules are transparent.

But exposing these lenses to UV light — specifically, UVA and UVB rays — triggers a fascinating chemical process. The molecules change shape, which allows them to absorb portions of visible light. In other words, your lenses darken.


Heading back indoors? The absence of UV rays initiates another chemical reaction, making the molecules revert to their original transparent state. This allows your lenses to change back to clear almost instantly.

Innovations in Photochromic Technology

Advanced Lens Materials and Absorption Techniques

Originally, photochromic molecules were evenly scattered in glass lenses. However, as plastic lenses gained popularity, the absorption method changed. Now, these molecules are absorbed up to a depth of 150 microns into the plastic, making the darkening process more effective.

Anti-Reflective Coatings and More

Today's photochromic lenses often come with extra features like anti-reflective coatings and blue light filters, making them more versatile than ever.



Should You Opt for Photochromic Lenses?

Variable tint lenses are available in both prescription and non-prescription forms, providing a cost-effective alternative to owning separate pairs of glasses for different lighting conditions.

However, these light-adaptive lenses are most effective in bright sunlight but may have limitations in variable light conditions or against reflective glare.


It's also worth noting that in colder temperatures, photochromic lenses actually darken more effectively, providing enhanced UV protection during winter months.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.


Frequently Answered Questions

How can I make my transition lenses darker without sun?
The easiest way to make your transition lenses darker without sun is to put on a pair of sunglasses over top. This will block the light and make the lenses appear darker.