Photochromic Lenses: How Do They Work?

Photochromic Lenses: How Do They Work?

Looking for a way to simplify your life (or just a way to deal with continually forgetting your eyeglasses or sunglasses)? Photochromic lenses might be a good solution. If you aren’t in the know about what they are or how they work, fear not. The eyewear experts at Stoggles have everything you need to know about them to decide if they’re right for you — plus, we’ll talk about our own version of photochromic lenses, our Stoggles Dimmers®. 

We’ll explain what they are, how they work, and compare them to a few other types of protective eyewear options. Once you’re done reading, you can tell everyone you’ve “done your research” and impress them with your spectacular spectacle knowledge. Get ready, we’re about to transition. 

What Are Photochromic Lenses?

Photochromic lenses (aka Transitions® lenses, a particular brand of photochromic lenses) are eyewear lenses that darken when exposed to ultraviolet light and fade back to clear when the ultraviolet light dissipates. That means the wearer of these Clark Kent-to-Superman styles glasses only needs one pair of specs for inside and outdoors. 

Having one pair of glasses that does double duty sounds like a huge benefit, and it can be, but let’s first understand what they don’t do.

What Aren’t Photochromic Lenses?

There are numerous types of eyewear lenses available, with features that can do everything from intrusive light to keeping your eyes safe from splashes, splatters, and spills. It’s easy to get certain types of lenses confused. 

Photochromic eyewear often gets confused with several different types of lenses, like the ones below. 

  • Progressive lenses. Progressive lenses are not photochromic lenses. Progressive lenses essentially replaced bifocals by offering multi-focal vision-correct in one single lens, without visible lines that delineate them. 
  • Polarized lenses. Polarized lenses offer a specific type of light filtration. These lenses are coated in a special chemical that blocks wavelengths of light that vibrates in a certain direction. They’re often used for reducing glare. 
  • Sunglasses. Regular sunglasses and photochromic lenses are different from one another. Sunglasses filter out certain types of light by using lenses of particular colors. Some sunglasses don’t offer UV protection, either, which is important to determine before you buy the eyewear. 

All of these types of glasses may be available with photochromic lenses, but by themselves, they don’t automatically have photochromic features. Now, let’s dive a little deeper into how photochromic lenses actually work. 

How Do Photochromic Lenses Work?

It’s all science. Light-sensitive molecules contained inside the lens change when exposed to UV light. This change in their molecular structure allows them to absorb more light when they are subjected to UV rays, and the lens naturally darkens. 

When the lenses are no longer exposed to these UV light conditions, they naturally fade back to clear. 

Three Important Factors

There are three factors that affect how photochromic lenses perform. Each of these factors plays a role in how well your photochromic lenses respond to the sun’s UVA and UVB rays and determines how well they will transition back to clear when they are no longer exposed to that light: 

Presence of UV light. When there is a higher presence of bright light from UV rays, the lenses transition faster. With less light (like on a cloudy day), the transition is slower. 

Amount of UV light. The amount of UV light your eyewear is exposed to is also a factor. For instance, if you are outside on a sunny day but seated in the shade, your lenses may not darken as much.

Likewise, if you are seated indoors by a window with plenty of sunlight pouring in, your lenses may darken.

Temperature. Photochromic lenses also respond to heat and cold. When it’s hot, they take longer to darken and clear up more quickly. When it’s cold, they will darken quickly and clear slowly. 

These factors are important because they play a big role in the pros and cons of owning a pair of these light-adaptive lenses, which we’ll cover later. First, let’s look at the product specs. 

What Materials Are Used for Photochromic Lenses?

There are two types of materials used to make photochromic lenses. 


Glass is no longer used as the predominant means of making photochromic glasses, however, they are still used by some manufacturers and are the first to have been invented. 

Glass is tempered with silver halide crystals. The most common type of silver halide used in lens material is silver chloride. When UV light hits the silver halide, the silver gains an additional electron which allows it to absorb more visible light. 

Photochromic glass is also tempered with another compound that allows it to readjust back to clear. Most commonly, copper chloride is used. Copper takes back the additional electron from the silver and returns the glass to its clear state. 

Glass takes longer to respond and is not as effective as the use of plastic in photochromic eyewear. 


Plastic photochromic molecules are made from carbon-based compounds that change in structure when exposed to UV light. These molecules are sometimes referred to as photochromic dyes. They’re more reactive than the compounds in glass lenses, which is why they function better. 

When exposed to UV light, the bond between the carbon compounds breaks, allowing them to absorb light. When the UV light fades, the dyes rebond, and the lens becomes clear again. 

Plastic is more cost-effective, lighter in weight, and more responsive than glass photochromic lens options. 

Now that you know the science behind these types of lenses, let’s weigh the pros and cons of owning a pair. 

Are Photochromic Lenses Worth It?

We love a double-duty product, and combining your sunglasses with your eyeglasses can be a great solution for people who wear prescription glasses, giving you one less item to keep up with. Some of the most valuable benefits of wearing these chameleons are:

  1. They eliminate the need for two pairs of specs. If you typically buy a pair of prescription sunglasses in addition to your regular eyeglasses, you’d only need one pair of photochromic lenses. 

  2. They offer constant UV protection. An important note, however, is that you should always check the lens brand to determine the level of UV protection you’re getting.

  3. They filter blue light. Most sunglasses don’t offer blue light filtering protection, but photochromic lenses usually do. This is a great option since blue light comes from both the sun and from devices. 

  4. They’re available in attractive frames and are much more durable than standard sunglasses. 

As with most things, there’s always a flip side. Here are some important factors to consider if you plan on swapping out your clear lens eyewear for a pair of photochromic lenses. 

  1. Even though technology has advanced, the transition time of your lenses may be longer than you expect, especially if you are in cold weather. 

  2. They eventually wear out. After about three years of use, your lenses will need to be replaced. The lenses themselves will begin to yellow, and the transition time will become slower and slower. 

  3. They are affected by temperature. Different climates may present a problem for getting your photochromic lenses to transition as quickly as you want them to. 

  4. You probably can’t wear them inside your car. Your car’s windshield already has a UV-blocking, anti-reflective coating on the windshield. This will mean that even if you’re driving in bright sunlight, your eyewear won’t darken. You’ll need separate shades for the car. 

There’s a case for owning a pair or not owning a pair of photochromic lenses. What is not optional is doing everything you can to protect your eyes from UV rays, blue light, and other hazards you probably haven’t considered.

Eye Safety

Nearly 700,000 Americans suffer eye injuries each year at work alone. Of the total amount of eye injuries, about half of them happen at home. Wearing intrusive-light-blocking eyewear is a step in the right direction for taking care of your eyes and protecting your vision, but it’s not the total package. 

What You Need

In terms of safety, you probably don’t need massive goggles that cover half your face and make it hard to focus on anything other than your massive goggles. Most people need the safety of reliable safety eyewear that has a few key features:

Shatter Protection 

It only takes one pebble from the lawnmower, one splash from a cleaning solution, or one toy tossed by a tantrum-prone toddler to seriously injure your eyes. Shatterproof lenses keep your eyes safe. 

The gold standard in shatter resistance is the ANSI Z87.1-2020 certification which ensures your eyewear is protected against high-velocity impact. Stoggles, for example, are all tested to this standard. 

Light Protection 

You need both UV light protection and blue light protection to keep your eyes completely safe. Both UV and blue light are emitted from the sun, and both are capable of passing through your cornea and reaching your retina. 

Every pair of Stoggles offers both types of protection. Our eyewear is crafted from lightweight, polycarbonate material that is naturally UV-blocking. We inject blue light-blocking compounds into our lenses when we make them to ensure your eyes get the protection you need. 

All Around Safety

Regular eyewear can leave your eyes vulnerable in key areas, like the space above your brows and across your temples. Side and top shields are a low-profile way of keeping those areas safe. 

Bonus: Unlike wraparound safety eyewear, which can sometimes warp corrective vision prescriptions, top and side shields don’t interfere with your vision correction. 


Fogging eyewear is annoying and dangerous. Don’t play games with your eyesight, and don’t mess around with fog. At Stoggles, we stop fog dead in its tracks by coating our lenses with an anti-fogging compound that lasts for a really, really, really (we mean really) long time, and can withstand higher temperatures than regular anti-fog eyewear or lenses. 

These features create the perfect eye-safety scenario that can help you keep your vision and ensure the safety of your eyes. Wondering if Stoggles are available with photochromic lenses? Wonder no more. 

Stoggles Dimmers

Stoggles Dimmers are the solution for keeping your eyes incredibly safe and also enjoying the benefits of lenses that darken when exposed to UV light. You’ll get the exact same safety features you expect from Stoggles, with the added bonus of lenses that quickly transition from clear to dark and back again, depending on your UV light exposure. 

Stoggles: The Smart Way to Photochrome Your Life

Owning a pair of photochromic lenses might be the perfect solution for you, especially if you find you lose your sunglasses or regular eyewear frequently. Choosing Stoggles Dimmers is a smart decision, and one that will protect your eyes and your impeccable style. 

Check out our latest frames and styles, and throw some shade on your eyes. 


What Are Polarized Lenses For? | American Academy of Ophthalmology

How Do Photochromic (Photochromatic) Glasses Work? | Science ABC

Sunglasses With Transition Lenses: Pros and Cons | American Academy of Ophthalmology

Preventing Eye Injuries | Prevent

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