Photochromic Lenses: A to Z

Photochromic lenses, commonly known as “transition lenses”, are lenses that darken on exposure to specific types of light, most commonly ultraviolet (UV) radiation in sunlight. The darkening of these lenses is reversible; they return to their clear state when the UV light is no longer present. 

They provide convenience by eliminating the need to switch between regular glasses and sunglasses when transitioning between indoor and outdoor environments. They offer UV protection and reduce glare, making them popular choices for eyeglasses and sunglasses

At Mi Vision in San Antonio, we offer one hour service with one of the best photochromic lenses in the world and with the most blue filter blockage in the optical world: The “Zeiss photofusion X“. What’s more, we have exclusive online specials each month, like the one below!


(1 hr. service)

Exam + Frame + Zeiss Platinum Lenses: Blue Filter + Premium Antiglare + Photochromatic

On selected frames with photochromatic Zeiss photofusion technology, only on gray color, polycarbonate lighter & impact resistant, UV protection & one of best blue filter in the market, Zeiss Duravision Platinum anti-glare treatment, single vision lenses with the following prescription parameters: +/-4 sphere & up to -2 cylinder.  Not valid with any other offers, sales or vision insurance. Must mention this offer prior to purchase. Done in one hour, counting after you obtain your sales receipt. Any sales after 5pm will be complete by 11am next business day. Offer ends 03/31/2024

Alright, enough with the self promotion.


In this guide, we’ll delve into everything you need to know about photochromic lenses—from how they work to their benefits and even their slight limitations.

What Are Photochromic Lenses?

Photochromic lenses, also known as light-adaptive lenses, are specialized eyeglass lenses that automatically adjust their tint in response to UV light exposure. In simpler terms, they darken when exposed to sunlight and return to a clear state indoors or in low-light conditions.

How Do Photochromic Lenses Work?

It’s as easy as 1-2-3. Here’s how photochromic lenses work:

  1. A chemical reaction occurs— Photochromic lenses contain special molecules embedded within the lens material. These molecules undergo a chemical reaction when exposed to UV rays. 
  2. This reaction causes the molecules to change their structure, resulting in the darkening of the lenses — When exposed to UV light, the molecules change their structure (called “photochemical reaction”), causing the lens to darken.
  3. This darkening is proportional to the intensity of UV radiation – the stronger the UV light, the darker the lenses become. This is why photochromic lenses are often used as sunglasses, as they darken in response to sunlight.
  4. When UV light diminishes, it reverts back to clear – When the lenses are no longer exposed to UV light, such as when indoors or in low light conditions, the molecules gradually revert to their original state. As a result, the lenses become clear again.

The speed at which photochromic lenses darken and clear varies depending on factors such as the intensity of UV light, temperature, and the specific formulation of the photochromic molecules. Photochromic lenses usually darken within 30–60 seconds, and clear within 2-3 minutes (it takes a bit longer). 

Are Transition Lenses the Same as Photochromic Lenses?

In a nutshell: yes, they are essentially the same thing. Transition lenses are simply a specific brand of photochromic lenses. 

While “Transitions®” is a well-known brand name, the term “photochromic lenses” encompasses all lenses with light-adaptive properties.

These lenses, regardless of brand, share the fundamental trait of adjusting their tint in response to UV light exposure.

Whether branded or generic, photochromic lenses offer wearers the convenience and comfort of adaptable vision, making them a staple in the world of modern eyewear.

How Fast Do Photochromic Lenses Change From Dark To Clear?

Photochromic lenses seamlessly transition from clear to shaded (aka darken) within 30–60 seconds upon exposure to UV light. This rapid adjustment ensures wearers remain comfortably shielded from the sun’s rays, regardless of outdoor activities or environmental changes.


But what about when sunlight diminishes or when you go indoors?


To clear, it takes 2–3 minutes, on average. This efficient transition ensures uninterrupted visual clarity, facilitating a seamless transition between varying light environments.


Ongoing research aims to improve the speed at which photochromic lenses activate and clear. As technology advances, users can expect smoother transitions and faster adjustments in the near future, reinforcing the reliability and usefulness of these innovative optical solutions.

The Pros/Benefits of Photochromic Lenses

  1. Convenience:

Photochromic lenses offer the utmost convenience by adapting to changing light conditions. Whether stepping out into bright sunlight or returning indoors, the lenses adapt to the changing light conditions. No more swapping between prescription glasses and sunglasses—these lenses do the job effortlessly. Whether you’re indoors or outdoors, they’ve got you covered, making life a little easier for those who are always on the go.

  1. UV Protection:

One of the most significant benefits of photochromic lenses is their ability to block 100% of both UVA and UVB rays. This exceptional UV protection helps shield the eyes from harmful ultraviolet radiation, reducing the risk of UV-related eye conditions such as cataracts and macular degeneration. By wearing photochromic lenses, individuals can enjoy outdoor activities with confidence, knowing that their eyes are well-protected from the sun’s harmful rays.

  1. Blue Light Filtering:

In today’s digital age, we’re constantly exposed to blue light from screens—and that can take a toll on our eyes. Thankfully, photochromic lenses offer relief. These lenses effectively reduce exposure to harmful blue light emitted by digital screens, such as smartphones, computers, and tablets, as well as natural sunlight. By filtering out blue light, photochromic lenses help alleviate eye strain, improve visual comfort, and minimize glare, particularly during extended periods of screen use or outdoor activities.

  1. Fashionable:

Who says functionality can’t be fashionable? With photochromic lenses, you don’t have to choose between style and practicality. These lenses seamlessly blend into a variety of frame styles, allowing you to express your unique personality while enjoying all the benefits of light-adaptive technology. Plus, with tint options ranging from classic gray to trendy brown and even subtle green, you can customize your look to suit any mood or occasion.

  1. Durable:

Last but not least: durability. Photochromic lenses are built to last, thanks to their embedded photochromic molecules. Unlike flimsy coatings or treatments that wear off over time, these lenses maintain their effectiveness for the long haul, ensuring consistent light adaptation and UV protection with every wear.

Any Disadvantages of Photochromic Lenses?

Photochromic lenses offer numerous benefits such as reducing glare and protecting the eyes from harmful UV rays. However, they do come with a small amount of disadvantages:

Speed/Transition Time: Photochromic lenses may not transition quickly enough between light and dark environments, which some users may find inconvenient than instantly swapping to sunglasses. This can be particularly noticeable when moving between indoors and outdoors rapidly or in situations where lighting conditions change rapidly, such as driving through dappled sunlight.

Not Suitable for Driving: While photochromic lenses are designed to darken in response to UV light, they may not darken sufficiently behind the windshield of a car. Most windshields are treated to block UV radiation, which can prevent photochromic lenses from activating fully while driving.

Temperature Sensitivity: Photochromic lenses may not darken as effectively in colder temperatures. This can be a concern for people who live in colder climates or engage in outdoor activities during winter.

Get Photochromic Lenses At Mi Vision Eye Care in San Antonio, TX. Call or Book Online!

Schedule an appointment today to discover the convenience of photochromic lenses and experience exceptional eye care like never before at Mi Vision Eye Care. Call 210-923-2020 or book online!

As a locally owned family optometry practice, we take pride in serving patients of all ages throughout Bexar County and nearby areas, including Balcones Heights, Medical Center, Castle Hills, Leon Valley, and beyond.

With over 800 5-star reviews on Google, our commitment to excellence is unmatched. We accept walk-ins and offer ongoing specials & discounts, making superior eye care accessible to all in the San Antonio area.

We also offer a full array of other unique benefits, including 

  • Guaranteed glasses in under 1 hour or less, or pay NOTHING
  • Same-day eye exams
  • Extensive selection of designer frames from renowned brands like Cartier, Dior, and Gucci
  • Open 7 days a week (Saturdays & Sundays)
  • Over 5,000 prescription eyeglasses in stock
  • On-site state of the art optical lab
  • No dilation eye exams
  • Hablamos español
  • Latino-owned business
  • Veteran owned business
  • Most vision insurances accepted