What is the mechanism behind photochromic lenses?
It may appear as though photochromic lenses are transforming. One moment, you may be wearing regular spectacles with clear lenses, but as soon as the sunlight strikes them, they darken. In this way, you have changed from regular glasses to sunglasses in a matter of seconds.
The purpose of this guide is to explain how the magic trick works, as well as the benefits that can be gained from wearing sunglasses instead of glasses.
Photochromic lenses: what are they?
In essence, photochromic lenses combine the benefits of glasses and sunglasses in a single frame, as they remain transparent indoors and darken when exposed to ultraviolet light from the sun.
Originally, photochromic lenses were made of glass and were patented in the 1960s. Plastic versions were introduced in the 1980s and 1990s and are more commonly used today.
How Do Photochromatic Lenses Work?
Lenses that are photochromatic are the same as lenses that are photochromic: they darken automatically when exposed to ultraviolet light. “Photochromatic” is just a less common term for lenses of this type.
What Are Transition Lenses?
Despite the fact that Transitions® lenses are branded types of photochromic lenses, the transitions® brand name (short for Transitions Optical) is often regarded as synonymous with the overall product, just as Kleenex and tissue are. Additionally, transition lenses are often referred to as transition lenses when the “s” is omitted from Transitions®.
This article will be referred to as “photochromic lenses” rather than “transition lenses” in order to avoid confusion. We are referring to all photochromic lenses, not only those sold by Transitions®.
Photochromic lenses may also be referred to by other names.
In addition to photochromic lenses, light-adaptive lenses, variable tint lenses, light intelligent lenses, and even reactolights are some other names for photochromic lenses. Light-responsive lenses are our preferred term when we do not refer to them scientifically, since it neatly encapsulates what these lenses do: they automatically respond to UV light when it is present.
In the event that you have trouble remembering these terms, you may be able to get the point across by using the term “lens that changes with the sun.”
What are the workings of photochromic lenses?
Once the UV rays are gone, the light-sensitive molecules inside photochromic lenses revert back to their original state, allowing them to absorb more light. As soon as the UV light is gone, the process reverses.
The photochromic molecules are sensitive to both the amount of UV light and its presence. When exposed to a substantial amount of UV light, they will change their structure more rapidly, while if exposed to a small amount, they will change their structure more slowly. In the shade, your photochromic lenses may darken slightly less than they do when exposed to direct sunlight.
The photochromic lens will still darken even under overcast skies since UV light penetrates the clouds.
In order to understand how photochromic lenses work, you must consider that each material undergoes a slightly different chemical reaction.
What are the principles behind plastic photochromic lenses?
Similarly, the compounds that make up plastic photochromic lenses change their structural properties when exposed to UV light. These compounds have scary-long names such as pyridobenzoxazines and indenonaphthopyrans.
Those lenses react to light more quickly than their glass photochromic counterparts—you do not need to know how to pronounce them. A chemical bond within the dyes breaks when exposed to UV light, resulting in the dye changing into a molecule that is more light absorbing.
As a result of the increased light absorption, the lenses become darker, and voilà, your glasses have become sunglasses. When the UV light subsides, the dyes revert to their original form and the lenses become clear once again.
The use of plastic photochromic lenses has become more common than the use of glass ones in recent years, and research is continuing to determine how they can be further developed.
What are the properties of glass photochromic lenses?
In order for glass photochromic lenses to function, minute amounts of silver halide crystals (usually silver chloride) are distributed throughout the lens. Silver becomes elemental silver when ultraviolet light hits these chemical compounds, where it gains an electron. As silver molecules appear and absorb visible light, the lenses appear darker.
In much the same way as photographic film, certain silver halides can also be used to create photochromic lenses to darken and develop. However, unlike photographs, glass photochromic lenses can be restored to their original translucent nature.
In the absence of ultraviolet light, a second compound embedded in the glass (typically copper chloride) take back the electrons that have been transferred to the silver metal. This reverses the process, resulting in a transparent lens once again.
The use of glass photochromic lenses in eyewear is far less prevalent these days, but they were the catalyst for the development of future light-responsive glasses.
What is the response time of photochromic lenses?
A photochromic lens darkens in about 30 seconds when exposed to ultraviolet light, and it takes about two to three minutes to clear once it has been exposed to ultraviolet light.
Scientists are still working on improving the reactivity of photochromic dyes. It is possible that in the future, we may see lenses that activate and clear faster and faster.
What are the effects of temperature on photochromic lenses?
When it is colder, the photochromic lenses darken more deeply, but they take longer to clear up when it is hotter. Photochromic lenses darken or clear up at different rates. Since the molecules within them are more reactive when it is warmer, they will not darken quite as much, but they will clear up more quickly when it is warmer.
Are photochromic lenses prone to wear and tear?
After a while, your photochromic lenses will become less reactive to ultraviolet light and will take longer to change between their two states. Some photochromic lenses may also take on a yellowish tint that indicates their age. Nevertheless, they are still considered a long-term investment since most of them will last for at least three years.
Photochromic lenses have several advantages
We have compiled a list of the pros and cons of photochromic lenses below so you can decide if they are worth it and whether or not they are good for your eyes.
Cost-effective and convenient
Photochromic sunglasses provide the best of both worlds in a single frame, so you do not have to buy separate prescription glasses and sunglasses frames.
Photochromic lenses do not require sunglasses to be carried with you (and you will not have to worry about losing them); the cost for photochromic lenses is typically lower than that of a pair of prescription sunglasses.
Providing excellent UV protection
Besides reacting to ultraviolet light, photochromic lenses also shield your eyes from it! With photochromic lenses, you reduce the risk of developing cataracts due to UV exposure.
Filtering the blue light
Unlike lenses without photochromic properties, photochromic lenses reduce the amount of blue light transmitted through screens (and the sun). They are also resistant to scratches, anti-reflective, and superhydrophobic.
It’s a fashion statement
In addition to the ability to darken into a color other than grey, photochromic lenses can also be incorporated into the frames of your choice. The Warby Parker collection includes dark grey, brown, and green colors.
Their durability is unmatched
It is impossible to remove or rub off the photochromic molecules because they are embedded within the lenses themselves. They will remain effective for the duration of their natural lifespan.
Photochromic lenses have some disadvantages
There may also be some disadvantages to photochromic lenses, depending on your needs.
Activation may take some time
Some people prefer the relatively instant swap to separate sunglasses, and we don’t blame them. However, if you are extremely impatient, you may not want photochromic lenses. Their sensitivity to temperature can also delay their transformations.
While you are driving, they are probably not going to work
While you are driving, your photochromic lenses likely will not darken all the way due to the UV-blocking properties of the windshield.
What is the best time to wear photochromic lenses?
During activities during which your environment may change, photochromic lenses are ideal. For example, if you will eat lunch indoors then ride a bike or take a museum tour after a walk in the park, they may prove useful to you.
Moreover, they can be useful in situations in which your hands will be occupied, making it difficult to locate and put on separate sunglasses. Photochromic lenses can be extremely beneficial if you enjoy sports such as kayaking, cycling, running, paddle boarding, or any other activity in which your hands are continuously used.
In fact, some individuals wear photochromic lenses practically all the time, as their light-responsiveness allows them to adapt to their surroundings, ensuring that they are always prepared for sudden change in weather.
How Do You Choose the Right Type of Photochromic Glasses?
It is possible to add photochromic lenses to most types of prescription glasses. Depending on your eyeglass needs, you may be able to get single-vision lenses, progressive lenses, reading glasses, or non-prescription glasses with photochromic lenses.
Is it possible to obtain photochromic contact lenses?
In the same fashion as photochromic glasses lenses, Acuvue Oasys with Transitions are the first light-intelligent contact lenses. When exposed to UV or High Energy Visible (HEV) light, these contacts automatically darken. Once removed from the light source, they return to a clear state within 90 seconds.
Light-responsive photochromic lenses for a variety of lifestyles
Photochromic lenses are a trendy and convenient two-in-one solution for individuals who do not wish to carry multiple glasses frames around. The trick works best when you have a pair of transforming lenses to show off, so feel free to share the science behind them with others now that you understand their science.