Photochromic lenses are eyeglass lenses that are clear (or nearly clear) indoors and darken automatically when exposed to sunlight. This is the result of chemical responses to the presence of ultraviolet light.
The most popular brand of photochromic eyeglass lenses sold in the Singapore is Transitions Lenses. Because of this, some people — including some eye care practitioners — refer to photochromic lenses as "Transitions lenses". But there are other brands of photochromic lenses available as well.
Photochromic lenses are very useful for driving, sports, and outdoor activities. They can even cut down on the harmful glare of electronic devices.
How Do Photochromic Lenses Work?
Photochromic lenses work the way they do because the molecules that are responsible for the darkening of the lenses are activated by the ultraviolet radiation in sunlight. UV rays can penetrate clouds, which is why photochromic lenses are capable of darkening on cloudy days. Direct sunlight is not required for them to work.
They shield eyes from 100 percent of the harmful ultraviolet rays from the sun.
This mechanic is also used inside most windshield glasses in cars. Windshields are designed this way to help drivers see in sunny conditions. This also means that since the UV rays that enter a car are already filtered by the windshield, photochromic eyeglasses will not themselves darken. Very recent advancements in photochromic technology allow some brands of photochromic lenses to activate in both ultraviolet and visible light, so these eyeglasses will turn darker even in a car that has a UV-filtering windshield.
Photochromic lenses work via a chemical reaction in the lenses. They are made with trace amounts of silver chloride. When silver chloride is exposed to ultraviolet light, the silver molecules gain an electron from the chloride to become silver metal. This gives the lens the ability to absorb visible light, turning darker in the process.
The lenses are made out of similar chemical compounds as those used in the development of photographic film. While film exposure is made to be permanent, photochromic lenses are also made with copper chloride, which strips the silver of its chloride electron. This is what helps the lenses return to their original, non-absorbing state in the absence of ultraviolet light.
This method is used in all forms of eyewear that use photochromic lenses, such as high-index lenses, progressive lenses, and bifocals.
Many people choose to use anti-reflective coating on their photochromic lenses to enhance their performance. Anti-reflective coating allows a greater amount of light to pass through the lenses to provide sharper vision in low-light conditions, like driving at night. This also removes reflections of sunlight and other distractions from the reverse side of the lenses when conditions are bright.
For obvious reasons, photochromic lenses cost more than regular eyeglass lenses. But customers get the freedom to not have to carry a pair of prescription sunglasses whenever it is bright out.
Different Kinds of Photochromic Lenses
Popular brands of photochromic lenses sold in Singapore include:
Transitions Gen 8 — Transitions Gen 8 lenses, introduced in the United States in July 2019, are the fastest light-adaptive Transitions lenses available. Gen 8 lenses get darker and become clear again quicker — three minutes less for fade back than Transitions Signature lenses with Chromea7 technology and 30 percent less time for the lenses to activate.
Transitions XTRActive — These lenses were developed for wearers who are light-sensitive indoors and desire a darker lens when driving and outdoors. Transitions XTRActive lenses have slight tint indoors to keep your eyes comfortable when exposed to harsh lighting (fluorescent lights, digital devices).
Sensity — Another form of photochromic lens is produced by Hoya Vision Care. Their product is called Sensity. In addition to changing in different light conditions, these lenses change their clarity consistently in different climates and temperatures. Hoya Vision produces Sensity lenses in a variety of colors, designs, materials, and coatings for anti-reflection.
PhotoFusion — PhotoFusion lenses come out of Germany, where they are made by Carl Zeiss Vision. These lenses come in a neutral gray tint, which gives users accurate colour vision in all degrees of light. They are also designed to darken and lighten quickly
SunSensors — SunSensors are made of mid- and high-index plastic materials and are available in gray and brown tints in a variety of lens designs.
PhotoGray — These glass photochromic lenses offer superior scratch resistance but are significantly heavier and less impact resistant than other photochromic lenses.
Photochromic sunglasses
Photochromic sunglasses are primarily for outdoor wear. They are not as clear indoors as other photochromic lenses, but they provide extra comfort in bright sunlight and behind the wheel.
Transitions Drivewear — These are polarized photocromic adaptive lenses that are made specifically for use behind the wheel. They are designed to darken and clear with changing light conditions when inside a vehicle. They enhance contrast and improve clarity for driving.
Photochromic lenses and blue light
Besides protecting your eyes from glare outdoors, photochromic lenses offer an additional important benefit — they help protect your eyes from harmful blue light.
Blue light contributes to digital eye strain and causes oxidative stress in the retina. It's even possible that long-term exposure to harmful blue light from sunlight and the display screens of computers, smartphones and other digital devices may increase a person's risk of macular degeneration and other eye problems later in life.
Visit us to discuss your blue light exposure risks and which type and brand of photochromic lenses is best for your specific needs.
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