The word ‘photochromic’ is coined from two Greek words: photos, meaning light and chroma, meaning color. Therefore, we can deduce that photochromic glasses can change their color when exposed to light. This is a very simplified definition of what photochromic sunglasses can do.

This article explains what photochromic glasses are, how they work, and what materials are used in their production.

What are Photochromic Glass Lenses and Sunglasses?
 

First developed in the 1960s by the Corning Glass Works factory, photochromic glass lenses are coated with chemicals which make them darker when exposed to bright light and clear when in normal light. These lenses are called several names, including ‘light intelligent’ and ‘variable tint’ lenses. Photochromic lenses not only block light, but they also protect the eyes and their surrounding tissues from UVA and UVB rays.

Photochromic eyewear comes in several forms, including contact lenses, prescribed eyeglasses, and sunglasses. Our focus here will be on photochromic sunglasses. Photochromic sunglasses are not as clear indoors as other photochromic eyepieces but get darker in the sun, blocking more light.

How Photochromic Sunglasses Work
 

A photochromic lens is usually coated or infused with organic and inorganic chemicals such as silver halide, pyrido-benzoxazines, and silver chloride. The molecules of these chemicals have a certain arrangement when under normal lighting conditions. When exposed to UV rays from the sun, these molecules move, rearrange themselves, absorb light, and the lens becomes darker as a result.

Although photochromic sunglasses mainly shield our eyes from very strong light, most are sensitive to ultraviolet rays and not visible light. That is why most lenses typically do not darken inside a vehicle because the windshield only lets in visible light while blocking most UV rays. However, newer technology allows some lenses, like those used in Maat Optical sunglasses, to activate with visible and ultraviolet light.

Recent advances in technology allow the addition of dyes to the coating materials, which lets you tint the eyeglasses according to your preferences. Photochromic lenses usually take around 30 seconds to darken when exposed to the sun and stay dark unless you move away from the bright area. It takes longer for the sunglasses to return to normal, typically around 2-5 minutes after leaving the sun. Environmental factors, such as temperature, can affect the time the lens takes to return to normal.

Types of Photochromic Lenses
 

Photochromic lenses were originally made with glass. However, the increased availability of other materials like resin or plastic has made the creation of sunglasses with other materials possible. Materials like plastics and resins are sometimes preferred to glass because they are more flexible and lighter in weight. Maat Optical sunglasses use glass and other high-quality materials so that you can make your choice based on your preferences.

Glass Photochromic Lenses

These are the original photochromic lenses. They use glass lenses coated with a photochromic chemical such as silver halide or silver chloride. Glass lenses are generally thinner and more attractive than plastic lenses because of their higher refracting indexes. However, they may be prone to producing glares.

Glass lenses are more scratch-resistant than lens materials like plastics. The major disadvantage of glass lenses is their brittleness, which decreases their durability. Also, glass lenses have a limited option of frames compared to other materials.

Plastic Photochromic Lenses
 

Plastic photochromic lenses use carbon-based compounds called photochromic dyes. When exposed to ultraviolet light, these compounds change their structure to darken the lens. These compounds, such as pyrido-benzoxazines, react more quickly to UV light than those used in glass lenses.

Plastic lenses are lighter than glass lenses, so they are more comfortable to wear and won’t slide down your nose easily. Plastic lenses are less prone to glare, more flexible and durable, and compatible with a wide range of frames. However, they are more prone to scratches and are usually thicker and less attractive than glass lenses.

Tinted Photochromic Lenses
 

The photochromic dyes used in plastic lenses can produce different colors or tints in sunglasses using plastic lenses. This gives you the flexibility to choose any color you like. The lenses can also be coated with an extra reflective compound, which offers more protection from UVA and UVB rays from the sun.

Benefits of Photochromic Sunglasses

UV Protection

A lifetime exposure to UV radiation and sunlight has long been associated with cataracts in older people. 

Photochromic sunglasses can effectively prevent up to of these harmful rays from reaching the eye.

Reduced Eye Strain 

By reducing the amount of light getting to the eyes, these sunglasses help reduce eye strain from bright sunlight. This leads to increased visual comfort when you’re outdoors.

Convenience

A photochromic sunglass is essentially two glasses in one: a pair of sunglasses in the sun and a normal pair of glasses in normal light. With these glasses, you need not worry about your itinerary because they work well indoors and outdoors.

Cost-Effectiveness

With photochromic glasses, you essentially get two pairs of glasses at a much lower price.

Disadvantages of Photochromic Lenses

Slower Response Time

Photochromic glasses take some time to adapt to new lighting conditions. It can be faster to whip out a suitable pair of glasses instead.

Higher Cost

Photochromic sunglasses cost more than conventional sunglasses. However, they cost less than getting two pairs of eyeglasses.

Temperature Sensitivity

The change in the molecules’ positions is a chemical reaction affected by ambient temperature. Cold or hot temperatures can make the lens transition more slowly than normal.

Not Safe for Driving

Photochromic sunglasses get darker when they come in contact with sunlight. Therefore, they should not be used while driving.

Conclusion

Among the brands producing photochromic lenses, Maat Optical can be considered one of the best. Our line of photochromic sunglasses has been designed to satisfy all your needs in a perfect pair of eyeglasses, such as comfort, optimum vision, and protection throughout the day.