20 Jun 2014

Why are trail runners buying photochromic lenses for their sports sunglasses?

Frankly, I am surprised that photochromic lens options available with the best sports sunglasses are so popular with trail runners.

I have to admit I was not a big fan of photochromic lenses in running sunglasses, so when my wife and co-founder of AMO gave me a pair to try on a trail run this weekend my immediate reaction was that I did not need them.

There, I have got that off my chest!

Last Saturday afternoon I went for a 26 km trail run, which started at 4.18 pm. I had left it late because it was June (mid summer in Hong Kong where I live) and hot. I wanted to go on a long steady run and not suffer.

I knew the route well. The first part was a country road for 6 km and then I hit the trails with a magnificent coastal run with cliffs below and some of the best beaches in Hong Kong for about 6 km where I hoped to time just before dark, then on some decent trails for the remaining 18 km - in both trees and the open.

'This is my gym!': Tai Long Wan'This is my gym!': Tai Long Wan

If you live in or know Hong Kong I started at Pak Tam Au barrier in Sai Kung country park and ran to Sai Wan then connected on to stages 2 and 3 of the Macleose Trail, eventually finishing at Kei Ling Ha.

I am a keen trail and ultra runner and I design and test sports sunglasses, so it seemed like a perfect opportunity to test AMO's new photochromic lens.

For those who don't know what photochromic lenses are, they are ones which change their shade on exposure to UV light. Basically they go lighter and darker in the sun.

AMO's photochromic lenses will darken significantly in one minute and then continue to darken very slightly over the next 15 minutes.

For the run I decided to wear the matt black AMO Ironcatcher sports sunglasses with an NXT Trivex® lens, tint category 1-2 (low to medium light).

Ironcatcher (Transformer series) fitted with an NXT Photochromic Low Light LensIroncatcher (Transformer series) fitted with an NXT Photochromic Low Light Lens

The trail run took me about 3 hours 45 minutes and this is what I learnt.

Field test: Photochromic lenses in running sunglasses

Before I set off I checked the time of the sunset. It was close to mid summer and it was going to set at 7.08 pm. After that I figured I would have another 15 minutes before I needed a torch.

1. TIME: 4.18 to 5.18 pm - good light

The initial part of the run was 6 km along a concrete country road. It was still hot and fairly well exposed to sunlight. During this time I was pushing the pace as my wife had set off 20 minutes ahead of me and I was determined to catch her.

The sun was still up although the day was cooling and my sunglasses felt like normal sunglasses: they were tinted but not excessively so and I was not squinting behind them.

The visibility of the NXT lenses was superb and they felt comfortable.

2. TIME: 5.18 to 6.18 pm - getting dark

After about an hour I began hit the coast and the nicest part of the run. The sun was getting low but visibility was still good. My lenses were still tinted but not excessively so and I had no trouble picking out the trail.

The slight yellow tint to the lenses made the evening sun appear brighter than it actually was as I passed by some of the most beautiful and iconic beaches of Sai Wan and Dai Long Wan.

AMO co-founder, Tim Hallworth, in 'his gym'!AMO co-founder, Tim Hallworth, in 'his gym'!

People were setting up to camp the night on the beaches or looking tired and heading home and I loved the interaction with the people on this stage of the run.

I was particularly impressed by how clear the lenses were and by now I was sweating a bit but the hydrophobic (water shedding) coating on the lenses was doing its job of keeping the lenses clear.

3: TIME 6.18 to 7.02 pm - just before dark now

Around this time I caught my wife who decided to cut the run short and run to the car. For me, the day was cooling off and I was feeling good. So with a water stop I set out in the final section (Macleose Trail - stage 3).

The initial part was a steep climb through trees up steps which I call "stairs from hell". It's a tough 18 minute climb to about 320 m and in the heat can break people. I had done about 16 km of undulating trails by now and was starting to feel a bit tired but after a GU was feeling much better.

By this time the sun was behind the bigger mountains creating a deep shadow. In parts I was bathed in the last rays of the day as the sun had not completely set and in some sections there was bright light coming almost horizontally at me. Definitely intermittent dark and light patches. In this situation the photochromic lenses really excelled. They lightened when I was in shadow and darkened when in low light.

The other remarkable thing was this was really where the yellow lens started to make a difference. The idea of a yellow lens is that it improves contrast and this was noticeable.

I was on rocky trails and even in the low light with the sunglasses on I could still make out the rocks and contours of the trail.

Through a photochromic lens at duskThrough a photochromic lens at dusk

I wore the sunglasses until 7.02 when the sun had dropped behind the mountains and it was quite dark. I then realised I was wrong about getting another 15 minutes of light after sunset (this may be right at sea level)!

4. 7.02 pm to the end

By this stage it was too dark to wear sports sunglasses and as the lens I had chosen had a grade 1 tint, I took them off and carried on my run with a torch.

Thoughts on photochromic lenses in running sunglasses

I have to say I was impressed. For most of the run I did not know that I was wearing sports sunglasses. As I write this I’m having to think really hard about the sunglasses and the lighting conditions which is one of the best compliments that anyone can make about sports sunglasses.

It seems that photochromic lenses really are suitable for trail running and I can understand why they are so popular. They are perfectly suited for this type of run and I now have to add them to my collection.

As a reward for reading this far, AMO sunglasses are offering you an additional 10% discount if you purchase a new pair of AMO sports sunglasses. Just enter discount code "BLOG106" at the AMO Shop



The sports sunglasses featured in this report are Ironcatcher (from AMO's Transformer series), fitted with an NXT Photochromic Low Light Lens, which is availble as an optional extra with Ironcatchers. Ironcatcher is available online at and the NXT Photochromic Lens option can be added curing the checkout process.

Tim Hallworth is a triathlete, adventure racer and ultra marathon runner and together with his wife Fenny is the co-founder of AMO Sunglasses.


  • Comment Link larin chat 123 3 Apr 2015 posted by larin chat 123

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  • Comment Link Lena 21 Jun 2014 posted by Lena

    I've been wearing photochromic lenses for over 4 years for running, they're ideal here in the UK where the weather is changeable. I also use them for cycling and everyday use.

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The AMO range...

Thunderstorm series

Protection and clarity for cyclists, mountain bikers and triathletes

Firestorm (red) - pictured with mirror-finish medium-dark lens. Also available in Snowstorm (white), Twister (green)


Typhoon series

Lightweight and comfort for ultra runners, marathon runners, cyclists and triathletes

Nimbus (white) - pictured with optional NXT polarised dark lens. Also available in Cirrus (yellow), Gale (pink)


Transformer series

Strong and lightweight for multisports athletes including ultra runners, marathon runners, cyclists, mountain bikers and triathletes

Ironcatcher (black) - pictured with Revo blue lens. Also available in Prowler (white)


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