Photochromic lenses are one of your options when selecting eyeglasses. They’re the type of lens that transitions to a darker color when exposed to the sun or other sources of UV light.
Other names for photochromic lenses include:
- Transition lenses
- Light adaptive lenses
- Variable tint lenses
What Are Photochromic Lenses Used For?
Photochromic lenses are ideal for people who need to wear glasses all of the time. The two main purposes of photochromic lenses are to protect your eyes from UV light and to eliminate the need for a separate pair of prescription sunglasses.
The lenses provide complete protection from UVA and UVB rays at all times. This protective feature doesn’t depend on whether the lenses are clear or dark at any given moment.
UVA and UVB rays are the two types of UV light that can get through Earth’s atmosphere. They’re the main types that should concern you when it comes to your health.
How Can UV Light Damage Your Eyes?
You’re repeatedly exposed to UV light throughout your lifetime, mainly in the form of sunlight. Over the course of your life, UV light can damage your eyes and the skin that surrounds them. This means that it’s important to protect your eyes by using products like photochromic lenses.
The types of eye damage that repeated UV exposure can lead to include:
- Cataracts. The lenses in your eyes become cloudy and increasingly more opaque with this condition. Cataracts eventually lead to blindness. You need surgery to treat this condition.
- Macular degeneration. This is a major cause of blindness in people who are older than 55. It’s the result of accumulated eye damage throughout your lifetime. There currently isn’t a cure.
- Corneal damage. Your cornea is crucial for proper vision. UV lightwaves can particularly damage this part of your eye.
- Skin damage. The skin surrounding your eye is vulnerable to UV damage as well. Examples of skin problems caused by UV include dryness, wrinkles, a loss of elasticity, and mottled pigmentation.
- Certain cancers. UV light interferes with the base pairs that make up your DNA. This leads to mutations that could cause cancer. Squamous cell carcinomas are an example of a type of cancer that can invade your eye. Eventually, this type of cancer can lead to the surgical removal of your entire eye.
How Do Photochromic Lenses Work?
Photochromic lenses have existed in one form or another since the 1960s. The technology has changed a lot since then, but the fundamental principles remain the same.
In general, these lenses work by using chemical reactions that are triggered by UV exposure. The result of the chemical reaction is a color change in the lens.
The very first photochromic lenses were made of glass and coated with silver chloride and silver halide, among other molecules. These silver compounds underwent a chemical change when they interacted with waves of UV light. The chemical change caused them to darken. The reaction reversed when the UV light was gone.
Today, the lenses are made from several different materials. Proprietary photochromic dyes are added to these materials in a variety of ways. The molecules within these dyes undergo color changes at different rates when exposed to UV light.
The lenses should darken in proportion to the amount of UV light they receive. This means that the brighter it is in your environment, the darker your lenses become.
What Are Photochromic Lenses Made Of?
These days, glass lenses are far less common than newer synthetic materials. Most lenses are made from some type of plastic or resin. The reason for this transition is that resins tend to be lighter and sturdier than glass. They’re also harder to scratch and easier to evenly coat or infuse with the photochromic molecules.
There are many ways to produce resins and infuse them with the necessary dyes. This makes them a more flexible material to work with compared to glass.
There are a variety of brands of photochromic lenses to choose from. Different brands construct their lenses from different base materials and dyes. So — even though all photochromic lenses work in approximately the same way — the variations in materials alter the characteristics of the lenses, including their rate of color change.
The frames for your lenses can come in all types of materials, including metal and plastic.
What Types of Photochromic Glasses Can You Get?
Today, there are a wide variety of photochromic lenses on the market. You can get them in an array of styles designed to fit your needs. Examples include:
- Sports eyewear. Only certain types of eyewear are safe to use during athletic events. These include polycarbonate and trivex materials. Transition lenses are available in both varieties.
- Coated lenses. Photochromic lenses don’t interfere with the particular types of coating that people like to have on their lenses. For example, anti-reflective coatings help reduce glare and are good for night driving. Water-repellant treatments prevent your lenses from misting over when you move from the cold outdoors to warm indoor environments.
- Colorful lenses. Traditional photochromic lenses were only available with a gray tint. But normal sunglasses can come in a wide range of colors. These days, you can get photochromic lenses that are brown or green. The range is still not as broad as for traditional sunglasses, so they may not be available in your preferred color.
- Bifocal, multifocal, and high-index options. Certain lenses are designed to deal with particular vision problems. Photochromic lenses are available for most common types of vision-correcting eyewear. For example, bifocal versions help people who have a hard time seeing both far away and up close. High-index options are helpful for people who need strong prescriptions.
Are Photochromic Lenses Right for You?
Photochromic lenses aren’t right for everyone. There are a few pros and cons to consider before deciding that photochromic lenses are the best choice for your eyeglass needs.
Things to keep in mind include:
- Cost. Photochromic lenses tend to be more expensive than the alternatives. But they’re cheaper than buying a separate pair of prescription sunglasses along with your normal glasses.
- Inability to control their transition. You can’t control when the lenses transition. It simply depends on the amount of UV light they’re exposed to. This can be a problem in places with bright fluorescent lights, which can cause your lenses to transition even though you’re indoors. The opposite problem can happen when you’re driving. Windshields are designed to block out UV light, so the lenses might not transition inside a car even when you want them to.
- Temperature effects. Colder temperatures cause some photochromic lenses to transition more slowly than normal. This can be frustrating in the winter.
- Blue light protection. These lenses do provide blue light protection as well as UV protection. This isn’t true for all lenses. Blue light comes from sources like phone and computer screens and is a common cause of digital eyestrain.