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:
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.
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:
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.
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.
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:
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:
American Academy of Opthalmology: “Sunglasses With Transition Lenses: Pros and Cons.”
Eye Care Trust: “Photochromic Lenses.”
Google Patents: “Method for manufacturing photochromic lenses.”
Johns Hopkins Medicine: “How to Protect Your Eyes from UV Damage.”
Optometrists Network: “What Are Transition Lenses?”
U.S. Food and Drug Administration: “Ultraviolet (UV) Radiation.”
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