A complete guide to photochromic sunglasses

Medically reviewed by Ing. Petra Průchová, Optometrist, on 11 Dec 2020. Written by Lentiamo

Photochromic lenses promise to protect our eyes from 100% of UV rays when they come into contact with sunlight. Otherwise, the lenses remain clear like typical glasses lenses. The lens changing process happens automatically when we go outdoors. There's no need to switch from prescription glasses to prescription sunglasses.

Curious to know how photochromic sunglasses work, what their benefits are, and whether you can get them even with a blue light filter? Then read the complete guide to photochromic sunglasses at Lentiamo.

What are photochromic sunglasses?

Photochromic lenses, also called variable tint lenses, are designed to react to ultraviolet light. The lenses darken in bright light conditions, i.e. in ultraviolet radiation. Without activation of UV light, the lenses remain in their clear state.

Photochrome sunglasses can provide a slight tint if required. They change their colour depending on how bright the light is. Therefore, photochromic shades will only darken very slightly in certain situations, e.g. when the room is brightened by sunlight.

Coupled with 100% UV protection, transition sunglasses ensure that your eyes stay comfortable and healthy all year round.

They are not only useful for everyday activities, but also for sports. Sports sunglasses with 400 nm protection keep you safe from the bright sun. You can use them outdoors, e.g. when golfing, cycling, fishing, skiing, running, and tennis, without sacrificing visual comfort and UV protection.

How do photochromic lenses work?

Photochromatic materials work with molecules within the material itself. The silver halide and silver chloride molecules are responsible for the lenses to change colour so that they can darken in bright light conditions and clear indoors.

When the sunglasses lenses are exposed to UV light, trillions of photochromic molecules begin to temporarily change structure. Once the shape of a huge number of molecules changes simultaneously, the surface of the lens darkens.

The result is a pair of glasses that turns into photochromic sunglasses and then back to back, without any intervention other than bright sunlight.

How long does it take for photochromic sunglasses to change from light to dark?

When Corning Glass Works' first photochromic lenses were launched in 1964, the lenses started reacting to UVA and UVB light only after a few minutes and reached maximum darkness after 15 minutes. Later models still needed up to a minute to adapt to the lighting conditions.

Today there are several brands that make use of a very rapid photochromic technology. This state-of-the-art innovation enables the transition from clear to dark within seconds.

The chemical process works the other way round, too, if you move indoors from outdoors. The dark shade of the lens fades in the first few minutes inside and becomes clear.

Did you know? The same technology is available in contact lenses. The lens materials of the bi-weekly lenses Acuvue Oasys with Transitions react to sunlight in seconds. They offer 100% UV protection for the part of the eye where the contact lens is located (mainly the cornea and a very small part of the limbus). So it's important to remember the rest of the eye (the sclera) is not protected.

What are the advantages and disadvantages of photochromic sunglasses?

In order to make it easier for you to decide whether or not it is worthwhile for you to buy photochromic glasses, our opticians have summarised all the advantages and disadvantages of photochromic lenses.

The pros of photochromic lenses

Photochromic glasses are cost effective. If you are the proud owner of a pair of photochromic glasses, you don't need to purchase two glasses, i.e. sunglasses and normal glasses, but you get the best of both, combined in one effective solution.
Transitional lenses are the perfect companion for those who tend to be a little lazy or careless. Because with photochromic lenses you can see and work perfectly both indoors and outdoors AND you limit the risk of losing your glasses.
Photochromic glasses are available in a variety of styles because the lenses can be ground according to the shape of the frame.
Blue light filters can also be added to photochromic glasses lenses to add a different kind of protection from blue light.

The cons of photochromic lenses

One drawback of photochromic lenses is that they fade more slowly than they darken. It takes them on average between 20 to 30 seconds to clear, depending on the brand and the design.
Temperatures play a role in the efficiency of transition sunglasses. In a cold environment, the lens changes colours more slowly. In a warm environment, the colour change is faster and more intense. The intensity of the colouring is therefore related to the manufacturer, often to the temperature 21-23 °C.

Can I get photochromic sunglasses with a blue light filter?

Some photochromic lenses offer you protection not only against ultraviolet light but also against visible light, i.e. harmful blue light. Without protection, blue light waves reach our eyes unhindered for several hours every day, damaging our eye health. The light emitted by screens such as computers, tablets, mobile phones and televisions can cause digital eye strain, difficulty falling asleep and headaches.

These glasses give you perfect protection against harmful UV rays and screen light. The blue light filter in the lenses activates when you look at a digital screen. They provide 100% UVA / UVB protection and blue light protection.

Sources:

1. Vision Ease, https://www.visionease.com/…gebypage.pdf
2. NCBI, https://www.ncbi.nlm.nih.gov/…/PMC7259785/