Photochromic Transition Lenses Explained

What are Photochromic Lenses?

Photochromic lenses also known as transition lenses darken to a sunglasses tint when exposed to sunlight, or UV ultraviolet, and return to a clear state when indoors, away from UV light.

Often referred to as transitions or reactolights, photochromic lenses are made of many lens materials including plastic, glass or polycarbonate. They are typically used as sunglasses that conveniently switch from a clear lens indoors to a sunglasses depth tint when outdoors, and vice versa.

Photochromic lenses were created in the 1960s at the Corning Glass Works Inc., and became the first variable tint/photochromic lenses brought to the marketplace.

How Do Photochromic Lenses 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 Transitions Lenses 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.

Advantages & Disadvantages of Transitions?

Photochromic lenses are 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:

Advantages:

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

Disadvantages:

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 Lens Temperature Dependency:

Photochromic lenses change state in a chemical and thermal process which can be affected/limited by a process known as 'temperature dependency'.

In extreme heat, a photochromic lens is unlikely to achieve full sunglasses shade and may only achieve a 95% state of tint.

On the other hand, photochromic lenses will become very dark in a cold environment/weather conditions. Cold weather also increases the time taken to return to a clear shade.

Plastic Vs Glass:

Plastic photochromic lens molecules of silver and halide are usually layered or embedded evenly onto the surface of the lens providing an even shade of tint when darkening.

Glass photochromic lenses have the molecules contained within the glass and this can sometimes cause an uneven tinting effect on a lens with higher prescription due to the different thickness of the lens from one edge to the other.

Can I use Transitions for 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.

A new lens has been brought to the market that can react inside a car or behind the windscreen without UV rays and uses daylight alone to trigger the reaction. These lenses are known as 'transition drivewear lenses' which combine both photochromic and polarisation technology.

As the name suggests, they were invented for use in the car whilst driving and offer full protection from the suns glare during the day which makes them perfect for wearing whilst driving.

This image shows how transitions Drivewear photochromic lenses react in different conditions:

Different Photochromic Lens Options:

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

Latest Transitions Lenses 2023:

The optical industry is constantly improving and creating new lenses.

Here are some of the latest photochromic lens designs in 2023:

Everyday use:

Transitions VII / Signature:  

Transitions VII / Signature is a lens that is completely clear when indoors, away from UV, and changing to a dark shade when outdoors. 

Designed to be completely clear in indoor environments and at night while quickly adapting and darkening in bright sunny outdoor conditions.

Transitions VII are not suitable for driving as the windscreen blocks the UV required to transition the lens.

Driving:

Transitions XTRActive:  

Transitions XTRActive are designed to change to sunglasses when outdoors and are darker than typical lens, they also have a light tint indoors to shade from harsh lighting. 

XTRActive lenses are also designed to react inside the car and behind the windscreen to protect your eyes from harsh sunlight while driving.

Modern windscreens block UV light. Transitions XTRActive activate when driving to reduce sun glare. It does this by collecting extra energy in the lower end of the light spectrum.

Light protection. UVA and UVB light is 100% blocked, protecting wearers eyes at all times. Transitions XTRActive lenses blocks 88% of blue-violet light outdoors and 34% indoors.

Transitions XTRActive are available in three colours -

• Transitions XTRActive Brown
• Transitions XTRActive Graphite Green
• Transitions XTRActive Grey

Photochromic Lenses For Driving:

Transitions Drivewear   

Transitions Drivewear lenses have polarised and photochromic technology. The polarised filter reduces glare and reflections from the road and other reflective objects while the photochromic filter adjusts the colour and tint of the lenses to suit the driving conditions.

Drivewear lenses feature a green/yellow colour tint for use in low light and adjust to a darker red/brown colour tint for when light is at it's most excessive.

Transitions XTRActive 

Transitions XTRActive activate when driving to reduce sun glare. It does this by collecting extra energy in the lower end of the light spectrum.

Light protection. UVA and UVB light is 100% blocked, protecting wearers eyes at all times. Transitions XTRActive lenses blocks 88% of blue-violet light outdoors and 34% indoors.

Photochromic Lens Brands:

Popular brands of photochromic lenses sold in the UK include:

• Transitions Signature 
• Transitions XTRActive
• Transitions Style Colours  
• Sensity (Hoya Vision Care) 
• PhotoFusion (Carl Zeiss Vision)  
• ColorMatic (Rodenstock) 
• PhotoView (Signet Armorlite) 

Conclusion:

Transitions or Photochromic Lenses are a great way to protect your eyes, potentially reduce costs and add some convenience to your routine but to some they will be inconvenient or inadequate and not worth purchasing.

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

How To Buy Transitions or Photochromic Lenses: