These smart lenses, also known as reactolights, or photochromic glasses, are advanced light intelligent lenses designed to automatically adjust to changing light conditions. Seamlessly transitioning from clear indoors to dark outdoors, adapting to the surrounding light intensity.

Whether you're exposed to bright sunlight or moving indoors, transitions lenses provide optimal vision, eye comfort, and UV protection by darkening in sunlight and returning to clear in low-light or indoors.

How Do They Work?

Tiny molecules of silver halide and chloride are embedded within a photochromic lens which is invisible and clear until exposed to sunlight/UV rays.

A chemical process takes place when exposed to sunlight/UV and the molecules effectively move, change shape and absorb the light. This process changes the molecules and they darken to a sunglasses shade/tint.

The photochromic lens will remain in this 'darkened' sunglasses state whilst exposed to sunlight/UV and the molecules will reverse the process once the lenses are removed from the sunlight/UV rays returning to the original 'transparent/clear' lens.

How Long Do They Take To React?

They typically take around 30 seconds to fully darken and between two to five minutes to return to a clear state.

They will return to an almost clear state within two minutes and be fully clear within five minutes, however, excessively high or low temperatures can affect this timeframe.

Compare Transitions:

The optical industry is constantly improving, updating and creating new lenses.

There are 4 main different types of transition lenses offering different results for different needs and here are the latest options in 2025:

For Everyday Use:

1. Transitions Signature GEN S:

Engineered to provide your eyes with a better vision experience and protection, transitions signature GEN S are the latest transition lens and are perfect for everyday needs:

This image shows how drivewear lenses react in different light conditions:

Click to Learn More - Transitions Drivewear 

4. Transitions XTRActive Polarised:

Combining transitions & polarisation, transitions XTRActive polarized cost £200.00 and provide your eyes with superior extra protection while delivering sharper vision but are available in a grey colour only.

Click to Learn More - Transitions XTRActive Polarised

The Pro's & Con's:

These lenses can be an extremely convenient, cost effective and beneficial purchase for a number of reasons, although, there are some weaknesses.

There are pros and cons of photochromic lenses and sunglasses, including those listed below:

Benefits:

1. Reduced costs – buying a single pair of dual purpose photochromic glasses that can provide vision for both indoors when clear and providing sunglasses protection outside is more cost effective than buying two separate pairs.
2. UV protection - Photochromic lenses provide full protection against the harmful UV rays of the sun and direct exposure to sunlight can cause serious eye problems and in some cases blindness.
3. Convenience - You only need to own one pair of glasses for both indoors and outdoors in the sun as opposed to needing to switch between two pairs of regular glasses to sunglasses. You only need to remember to take one dual purpose pair of glasses with you as no doubt at some point we have all forgotten to take our sunglasses out with us only to be caught out by the glare of the sun or even left them behind never to be seen again.
4. Eye Health – Reducing your exposure to the suns harmful UV rays can lower the risk of cataracts or other eye/age related problems

Weaknesses:

1. Reaction Times – Although photo lenses reaction from clear to sunglasses is quite quick, typically within 30 – 60 secs, the reversal takes a little longer as much as 5 minutes depending upon the temperature of the lens which could be dangerous if entering a dark room or certainly inconvenient at best.
2. Driving – Standard photochromic lenses do not work inside a car due to the windscreen blocking out the UV rays which are needed to active the chemical process which causes the lens to darken. (Although there are special photochromic lenses that can react inside a car or behind glass which are specialist lenses known as 'transition drivewear lenses' which combine both photochromic and polarisation technology.
3. Not Dark Enough – Photochromic lenses as convenient as they are at blocking out UV rays and protecting you from the suns glare will likely not be sufficient for anybody who suffers from extreme high light conditions. Fortunately, the lenses are suitable for the majority of wearers but advice must be taken if you are affected by any light conditions.

Photochromic lenses are available in many lens types, materials, coatings and designs, such as varifocals, high index lenses and polarised lenses. 

'Transitions XTRActive Polarised' and 'transition drivewear lenses' both combine both photochromic and polarisation technology.

Lens Conclusion:

Having transition lenses in your frame can give you a convenient, 2 in 1 pair of glasses/sunglasses, reacting from clear to dark, as & when required. This also eliminates the need to carry 2 separate pairs of eyewear and maybe even saving you money on such costs.

However, to some they will be inconvenient or inadequate and not worth purchasing.

Ultimately, it's up to you to decide if transitions lenses will benefit you, but please feel free to contact us should you require any further information or advice. 

How To Buy: