Home Sunglasses Sunglasses Types

How do transition lenses work?

woman wearing transitions sunglasses looking up at the sun

Photochromic lenses, commonly known as transition lenses, are widely known for their ability to automatically darken in the presence of sunlight. But how do photochromic lenses work?

The mechanism behind photochromic lenses comes down to a little bit of good old-fashioned science. When the molecules in photochromic lenses are exposed to sunlight, they cause the lenses to darken.

Let’s explore more of the science behind this light-adjusting technology that available in eyeglasses, sunglasses and now contact lenses.

How do photochromic lenses darken?

Built into every transition lens are silver halide and chloride molecules that temporarily change their structure when when struck by the sun's UV rays.

When the structure of trillions of molecules changes at the same time, the entire surface of the lens appears to darken.

The end result is glasses that turn into sunglasses, then back again, with no intervention at all aside from sun exposure.

In the past, this process took up to a full minute to complete. But thanks to evolving technology, many photochromic lenses now transition from clear to completely darkened in as little as a few seconds.

The process works in reverse when you step inside from the bright light outdoors. The dark tint of your photochromic lenses fades to clear over your first few minutes inside.

The same technology that turns eyeglasses into sunglasses now is available to help contact lens wearers adapt to light. Acuvue OASYS with Transitions (the leading photochromic lenses brand in the U.S.) were introduced in April 2019.

Photochromic glasses tend to have a fully-functional lifespan of around two to three years, which is roughly the average lifespan of a specific eye prescription. However, individual photochromic lenses lifespans vary based on manufacturer, how often you wear them and how you use them.

When your photochromic lenses start to take longer and longer to transition from indoor to outdoor light, that's a sure sign it is time to get new transition lenses.

WANT TO TRY PHOTOCHROMIC LENSES (OR IS IT TIME TO GET NEW ONES)? Ask your eye doctor if photochromic lenses are right for you or add them to your glasses order online.

Find Eye Doctor

Schedule an exam.

Find an eye doctor near you.