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Photochromic vs. Polarised Lenses

Sunglasses are a versatile accessory; they protect your eyes and make you look cool. You may put a lot of thought into the frame of your glasses or sunglasses, but choosing the right lenses is just as important. With so many lenses available, it may be difficult to understand which are right for you. The best lenses for an individual will depend on your unique visual needs and what you hope to get from your shades. Photochromic and polarised lenses are two of the many lens choices which offer excellent UV protection, but many wonder, what exactly is the difference?

What is the difference between photochromic and polarised lenses?

Photochromic and polarised lenses both effectively protect your eyes from harmful UV rays. They're both available in a diverse range of frame styles and are highly beneficial to wearers. The difference? Simply put, photochromic lenses start clear and darken upon coming into contact with UV light. In contrast, polarised lenses are always tinted and have a special coating that's especially good at blocking glare.

What are photochromic lenses?

Photochromic lenses, also known as Transitions® lenses, are an excellent choice for people who are sick of switching between their prescription glasses and prescription sunglasses. As light conditions change, so do the lenses. And the best part, you never have to change your frames. Inside, away from UV light, photochromic lenses are clear, but as soon as you step outside and UV rays are present, they gradually darken.

Plastic photochromic lenses and glass photochromic lenses use the same technology but are a bit different in their composition. Plastic photochromic lenses include molecules of silver halide that are usually layered or embedded evenly onto the surface of the lens, providing an even tint when exposed to UV light conditions. Glass photochromic lenses contain the molecules within the glass. This can sometimes cause an irregular tint on lenses with a higher prescription due to the uneven thickness of the lens.

How do photochromic lenses work?

It's all about a chemical reaction. Photochromic lenses have light-sensitive molecules that shift their structure when combined with UV light. When this light is absorbed, the lenses darken. Away from the UV light, the process reverses, and the lenses become clear again. On average, photochromic lenses darken in 30–60 seconds and clear a bit slower in 2–3 minutes.

The molecules in photochromic lenses are not only sensitive to the presence of UV light but also the amount of it. A lot of UV light and they will change more quickly; less light and they'll change more slowly. If you find yourself in the shade, you might notice your lenses darkening less than in direct sunlight. UV light is still present in low light, overcast skies, causing photochromic lenses to darken even in these conditions. 

What are polarised lenses?

Polarised lenses are tinted lenses with a special coating that blocks glare, boosts visibility, increases clarity and enhances contrast to make your surroundings more vibrant. Polarised sunglasses are handy for people who spend a lot of time outdoors, as they block out reflections that come from rain, snow, or water. When the sun reflects off these surfaces, it causes a powerful, horizontal glare that may cause eye damage and strain.



How do polarised lenses work?

Polarised lenses are coated in a chemical filter that acts as a vertical blocker and won't allow any horizontal wavelengths through. When light hits a flat object, like a lake, ski slope, or metal sheet, the reflection is in a single, concentrated direction, creating a bright polarised glare. Polarised glare means the light waves are mostly aligned in one direction, in this case, horizontally. As polarised lenses are designed to block this horizontally polarised light, their chemical filter absorbs it, letting you see clearly.

Advantages and disadvantages of photochromic lenses

One of the biggest advantages is how cost-effective and convenient photochromic lenses can be. With no need for a separate pair, one pair of glasses acts as both your eyeglasses and sunglasses. Photochromic glasses prevent you from worrying about changing your glasses upon entering or exiting a building or the sunshine. Photochromic lenses are beneficial when the weather changes throughout the day; if the sun is going in and out of the clouds, you're on the slopes or hiking in the woods.

While photochromic glasses benefit many wearers, there are some disadvantages to consider. Temperature impacts the rate at which photochromic lenses darken or clear up. The lenses usually darken more fully in cold weather but take longer to clear. In warmer weather, they may not darken as much but will become clear quicker. Most photochromic lenses perform well for three-plus years, but eventually, they will become less reactive to light conditions and take longer to shift between clear and tinted. 

It is important to note that some photochromic lenses are unsuitable for driving because the car windshield blocks the UV rays that generally cause the lenses to adjust. Some models, including the Transitions XTRActive® lenses, have more photochromic molecules allowing them to transition even while in the car. These lenses always have a very light base tint and will not go as dark in the car as outdoors. 

Advantages and disadvantages of polarised lenses

Whether hiking, cycling, or boating, polarised sunglasses are a great option. The lenses are designed to reduce glare and enhance outdoor vision, helping improve performance while making colours look more vibrant. Polarised lenses are well suited for driving during the day, as glare from other cars, or the road is a common scenario. With reduced glare comes a lower risk of eye strain. Polarised lenses are an excellent solution for people with light sensitivity, and they may even be recommended to patients who have had cataract surgery.

With many advantages, there are some things to consider before buying polarised lenses. Polarised lenses may reduce vision clarity when looking at LCD screens or certain displays. For anyone working in a job where looking at display screens is expected, you should test polarised lenses before purchasing. 

While polarised lenses are beneficial in snowy conditions, they may make it harder to see patches of ice. If you're skiing, snowboarding, driving, or walking where there might be lots of ice, it may be best to avoid your polarised sunglasses and reach for another pair. Another disadvantage is that polarised lenses are always tinted, so if you wear prescription glasses, you will need to carry your glasses and sunglasses. 

Is photochromic or polarised better?

Photochromic and polarised lenses have distinct qualities and advantages, making them great options for your collection. Generally, neither is considered better than the other. Photochromic lenses are a great option for those who are always on the run, with one pair of glasses serving as eyeglasses and sunglasses. Polarised lenses block out glares and reflections, not only improving vision but providing a level of safety. 

Both lenses will protect your eyes from the sun's harmful ultraviolet light. The best choice is always individual, so it is encouraged that you review the functionalities, consider your environment and budget, and compare this to your lifestyle. If you still have questions, head to our Optical Centre and speak with one of our opticians. 

Photochromic or polarised lenses, which to buy?

Depending on what you use your sunglasses for, one may be a better choice than the other. If a reduction in glare will benefit your performance in fishing or cycling, for example, you may choose polarised lenses. Photochromic lenses may be best for you if you need a pair of sunglasses for everyday wear.

Lenses don't have to be complicated; consider the differences and your needs, so you can buy and wear what works for you. With so many options, it's always best to be informed about your choices. Learn more about lenses, and remember, whether you purchase photochromic or polarised, make sure they fit into frames that make you feel confident.