A Detailed Guide to Photochromic Lenses
For most people who have problems with their visual acuity, it can be cumbersome having to switch between glasses they use for their vision and sunglasses when they step out. This is where glasses made with photochromic lenses come in. They are sunglasses where the lens is made from a special material that is usually clear but darkens on exposure to sunlight. So your glasses adapt depending on the type of light it is around. For this reason, they are also called ‘light adaptive lenses’.
The Mechanism behind Photochromic Lenses
Eye glasses come in a wide range of materials and design in terms of both frames and the lens of the glasses. Like the frames, the lens can be made from a wide range of materials. These include glass and plastics. A polycarbonate is usually used as lenses in children’s glasses as they do not break easily. This can be beneficial as children are usually exposed to high impact collisions and falls during playing. Depending on the lens material, the working behind the darkening of the lens is different.
The lens usually darkens considerably within one minute of exposure to sunlight. It is the UV radiation in sunlight that causes the change to take place. This is reversible and when the stimulus i.e. UV radiation is removed it starts returning to its normal clear state.
In glass lenses, the photochromic property is achieved through incorporating silver halide into the glass lens. On exposure to the UV radiation in sunlight, these molecules of silver halide undergo a chemical reaction that causes them to form silver in its element form. This is what departs the “darkness’ to the lens.
In plastic lens, the darkening is achieved by UV radiation coming in contact with organic photochromic molecules. These molecules are usually present at the surface layer of the plastic lens.
The photochromic property can be found in a wide spectrum of lens types, from bifocals to progressive lenses. If the lens has anti-reflective coating it greatly augments the photochromic darkening process and helps with better vision at night. These lenses can work in cloudy weather conditions, as UV radiation, the agent behind the darkening, can still pass through clouds. They will however not darken, if you are inside a car. This is because most windshields considerably block out UV radiation.
Benefits of Photochromic Lenses
Ultraviolet light is made up of two kinds of radiation: UVA and UVB. Both UVA and UVB cause skin cancer. UVB can also cause the burning of skin. Almost all glass can stop UVB radiation from passing through but not UVA. These lenses are great because they can block out 100% of both UVA and UVB light. This means that it offers protection from burning and helps reduce the chance of developing skin cancer especially around the eyes.
UV radiation has also be one of the factors associated with the development of cataracts, especially with age. These lenses block UV radiation hence reducing the chance of developing cataracts. They also offer protection from blue light which has been linked to eye strain and oxidative stress in the retina.
While these lenses are costlier than their non-photochromic counterparts, it can be cheaper in the long run as you do not need to buy a separate pair of prescription sunglasses
Popular brands for Photochromic Lens
You might hear photochromic glasses referred to as ‘transition’ lenses, this is because the most popular brand known for making this light intelligent glass is Transitions Lenses. It is how Spandex has become synonymous with shape wear. The different ranges are:
- Transitions Gen 8: Introduced in the summer of 2019, these lenses are famous for their speed in color changing. It takes 30% lesser time to darken than Transitions lenses with Chromeao7 technology.
- Transitions XTRActive: These were designed for individuals that are exposed to harsh lighting indoor from fluorescent lights and electronic devices. These lenses are lightly tinted even while indoors.
- Transitions Vantage: Like those above, these are also slightly tinted while indoors. On going outside these lenses darken and polarize. The polarization helps reduce glare in bright reflective situations.
- Transitions Drivewear: These are photochromic sunglasses that are especially good while driving as they adapt to changing light conditions inside the car and offer an increase in contrast.
Corning is an American company that specializes in the production of ceramics and glass for industrial and scientific purposes. Their ranges are as follows:
- Sunsensors: These are plastic lenses in brown or grey colors available in a diverse range of designs
- PhotoGray; PhotoBrown: These offer the benefit of being highly resistant to scratches on its surface. However, these lenses are also more prone to breaking and weigh more than the average lens would.
- Thin and Dark: These lenses feature in a gray color. The company claims that these are lighter and thinner than the other similar lenses available in the market by up to 30%
Hoya Vision Care
When Hoya Vision care introduced their photochromic range Sensity in the April of 2016, they promised a lens that would work optimally offering a greater viewing experience in a wide range of climates and weather conditions.
This German company has a range of light adaptive lenses called ColorMatic. The lenses are offered in gray, brown and orange tints. You can also buy an orange and green contrast shade under their ColorMatic IQ Contrast line.
Carl Zeiss Vision
This is another German based company that offers PhotoVision as neutral gray tinted light-adaptive lenses. This range is better as compared to its previous range it can darken up to 20%
Their lenses range LifeRx use polycarbonate as lens material, hence offering high impact resistance. According to the company, they take less than a minute to darken.
Their photochromic range is PhotoView which offers lenses in brown and gray colors that can be incorporated in a cool range of designs, with the added benefit of being Kodak progressive lenses.