UNDERSTANDING PHOTOCHROMIC LENSES: HOW THEY WORK AND WHO THEY SUIT
Most glasses wearers are familiar with the everyday hassle of swapping between spectacles and sunglasses. It’s a small, common inconvenience that compounds over time – especially on days of changeable weather or if you’re constantly moving between different environments.
This is the struggle that photochromic lenses seek to solve. These lenses combine two functionalities in one, acting as regular, transparent prescription glasses while indoors and automatically darkening upon encountering ultraviolet light from the sun.
The major drawcard of this technology is convenience, eliminating the need to pause and switch between glasses and sunglasses throughout the day, particularly during activities where your hands are occupied. They also have long-term eye health benefits, blocking 100% of UVA and UVB rays, reducing cumulative UV exposure and therefore helping combat the risk of conditions such as cataracts.
Vision clarity and sun safety all in one frame – photochromic lenses are an incredible innovation that might seem like magic to the uninformed. So, how do they really work?
The Science Behind the Transition
Glass Lenses
Photochromic lenses have been around since the 1960s, originally constructed from glass but now more often made of plastic. Embedded within early glass lenses were miniscule crystals of silver halide that, when exposed to UV light, would undergo a chemical reaction during which they gain an electron and become elemental silver. As a result of these molecules changing shape, they are able to absorb visible light, creating the darkening effect across your photochromic lenses.
When heading back indoors, away from ultraviolet light, the process reverses. This is often facilitated by copper chloride compounds also distributed within the glass taking back the transferred electron from the silver, returning your lenses to transparency.
Plastic Lenses
Modern plastic lenses take a slightly different approach. Rather than silver ions, these lenses rely on carbon-based compounds (also known as photochromic dyes) absorbed up to a depth of 150 microns into the plastic. These complex organic molecules are engineered to change shape in the presence of UV light, the chemical bonds temporarily breaking to form an ‘open’ structure which allows visible light to be absorbed, darkening the lens.
In the absence of ultraviolet light, the molecules gradually revert to their original ‘closed’ structure, appearing clear once again – a process occurring repeatedly over the life of your photochromic glasses.
Plastic lenses are preferred in the current day for their lightweight design and improved reaction to light, the transition between dark and clear taking place faster than in original glass lenses.
How Long Does the Darkening Process Take?
On average, it takes around 30 – 60 seconds for photochromic lenses to darken when exposed to UV light, and 2 – 3 minutes to completely clear again. There are, however, factors which affect this transition.
Temperature can influence how quickly the molecules react and the intensity of the reaction. In warm weather, the molecules move faster, meaning that while the fading process is much faster, the lenses find it harder to remain in a darkened state, and may not reach their darkest potential tint. Meanwhile, in cooler temperatures, the molecules are moving slower, meaning a slower transition time but also a more effective activation, resulting in a deeper tint.
The amount of sunlight also impacts the darkness of the tint. UV light can penetrate clouds and reflect off surfaces, so you don’t need to be standing in direct sunlight for your photochromic glasses to darken. That said, less light will cause the sensitive molecules to change their shape slower, and you’ll likely notice a reduced tint while wearing your lenses in the shade as opposed to under full sun.
The Benefits of Photochromic Lenses
It’s easy to see the benefits of photochromic glasses over traditional spectacles and sunglasses, however, if you’re still on the fence, here are a few key points to keep in mind:
1. Versatility
Photochromic lenses are the definition of versatility, adaptable not only to the sun but also your style. Available in most prescriptions, choose between grey, green and brown tint options and pair your light-sensitive lenses with a frame of your choice to express yourself freely.
2. UV Protection
With UV-blocking properties built into the lens material itself, photochromic lenses help shield against harmful ultraviolet rays even while in their clear, inactive state. The darkening effect also acts to reduce glare and eye strain, enhancing visual comfort in bright conditions.
3. Convenience
With one pair of glasses to suit various environments, photochromic eyewear eliminates the need to switch between clear glasses and sunglasses, meaning you no longer have to carry around and keep track of multiple pairs.
4. Cost Effectiveness
By combining your prescription glasses and your sunglasses, photochromic glasses allow you to cut down on the number of frames you need to purchase, as well as lowering the risk of losing costly eyewear as you swap between pairs on bright days.
Keep in Mind...
Photochromic glasses are great, but it’s worth considering your own unique needs and preferences when deciding whether to invest in a pair. If patience is not one of your virtues, the gradual shifting nature of photochromic lenses may be more of a bother to you than a benefit.
While effective in bright sunlight, these light-adaptive lenses also have limitations in variable light conditions and against reflective glare, as well as inside a car. Modern vehicle windshields often have their own UV-blocking properties which can interfere with the effectiveness of some photochromic lenses, preventing full activation. Luckily, at Optical Superstore, we have a lens designed for this exact scenario…
Where Can You Find Photochromic Lenses?
Optical Superstore’s QuickTint range includes quality photochromic prescription lenses which can be inserted into any frame from our wide selection of exclusive and designer brands. Our friendly staff are always happy to help you find the ideal solution for your lifestyle.
- QuickTint
Designed to keep pace with your dynamic lifestyle, QuickTint lenses automatically adjust to changing light conditions while providing essential UV protection, and are available in grey, brown and green tints.
- QuickTint Extra
Experience all the same benefits of QuickTint with the added advantage of extra darkness outside and the ability to darken inside the car for reliable glare reduction behind the wheel.
But first, schedule an appointment with a qualified tenant optometrist at your nearest Optical Superstore to ensure your eyes are healthy and prescription is up to date so your new photochromic glasses can provide you with the best possible clarity!
The One Pair Solution
Photochromic lenses are a clever blend of chemistry and optical engineering, created to solve an issue of convenience that so many glasses-wearers contend with daily.
Come by your nearest Optical Superstore today to discover our versatile QuickTint photochromic range and invest in excellent vision clarity and comprehensive UV protection!
