Koo Eyewear Alibi sunglasses

The Koo Eyewear Alibi Sunglasses have a unisex half-frame design that's made to offer maximum visibility. Our test pair has a matt white frame and a fuchsia-coloured, fast-acting photochromic lens that's designed for year-round road and gravel riding. I found the lens superb for low-light conditions and suitable for all but the very brightest of summer days, and its high-quality lens is backed up with good comfort. But I do feel the Alibis are best suited to riders with smaller heads – and there is a definite knack to swapping the lens.

> Buy now: Koo Eyewear Alibi Sunglasses for £200 from Condor

I have to say that I really like the look of the Alibi sunglasses from Kask's sister company Koo. The lens changes colour as the ambient light lessens, becoming a translucent light-blue – which made me feel like a character straight out of a 1980s anime such as Battle of the Planets (Google is your friend if you don't know your Japanese popular culture...). And while the large lens means the glasses really do stand out, I did receive a lot of positive comments about them from fellow riders.

Koo makes a variety of lenses for its Alibis but ours came with a photochromic lens with a 1-3 filter category: 1 is pale for an overcast day and 3 is for bright conditions when the lens turns dark. The VLT (Visible Light Transmission) range of the lens is from 75% to 12%: during the dullest conditions it allows 75% of the light through, dropping down to just 12% when it's very bright.

The one-size-fits-all frame measures 142mm across the top of the lens, while the rounded arms are 110mm long. The frame is available in eight different colourways and is made from Grilamid, a thermoplastic material that Kask says is shock-resistant, light and non-allergenic.

I did find the textured arms quite stiff, and they feel tough too – though I wouldn't want to test the limits of their toughness by accidentally sitting on them. They grip very well though, and didn't budge or slip at all when I was riding on the drops. I could just about see the edges of the lens in my peripheral vision but not the Koo logo or the central support pillar.

In use

The Alibis are very light, weighing just 29g, and it barely felt like I was wearing them at all. There are a few small ventilation gaps between the top of the lens and the frame, which presumably accounts for the lack of any steaming up when I was puffing my way up my local climbs. And I found they successfully shrugged off light rain too.

I wore the Alibis with a variety of helmets – from Kask, Poc, Lazer and dhb – to check for any compatibility issues and had no problems with any of them. I'd say the frame size is probably better suited riders smaller or medium head sizes, and with a 60.5cm head circumference I think I was close to the upper limit for these.

The lens

I have to say that the highlight of the Alibi sunnies is the performance of the photochromic lens, which I found very effective in a wide range of lighting conditions – from darkness to daylight.

I was amazed to find I was able to wear these while cycling at night on the Sustrans Bristol and Bath Railway Path. I kept having to check that it wasn't affecting my night vision – but it really was very good wearing them in the dark.

They were especially welcome when riders with 2,000-lumen death-ray lights were heading in my direction, and they were similarly efficient at reducing glare from oncoming car headlights at full beam when I hit the road. For the tech-minded, I'd compare it with applying an 'easy eye' filter on a bright LCD computer monitor. And while my lens had a 12-75% VLT range, Koo also does one with a 15-87% range that would be intriguing to try out.

The glasses worked equally well in the sunshine too, with consistent colours across the lens – and the lens also reacts quickly, turning dark when you exit a tunnel or emerge from tree cover into bright sunshine.

I was testing these in winter, and on days when the sun was really low and I was riding directly towards it I was very glad to be wearing them. I think they might struggle in an absolutely clear sky under a blazing summer sun, but with the exception of days like that, I think these would be a great choice for the majority of year-round riding.

I did struggle with removing the lens at first, but I found there was a knack to it – you unclip the sides of the lens from the frame and then push the lens out from the central support piece. I eventually got the hang of it but it's not something I'd like to do very often, as I worry that I could damage what is a really nice lens.

Koo sells a few separates for its Alibis: spare photochromic or mirror-finish lenses cost £44.99, spare nose pads £8.50 and a clip for fitting prescription lenses is £50.

Value

While the Alibis are undeniably expensive – they're well made, have a premium feel and smart looks. And that price is comparable to those of other premium brands' photochromic glasses and the same as the top-priced sunnies in our best cycling sunglasses buyer's guide.

Anna Marie tested that £200 SunGod Airas Base Frame with a photochromic lens. The lens clarity and fit were excellent but they didn't quite protect from the wind as well as hoped.

Our sister site off.road.cc reviewed the Melon Optics Alleycat glasses, with a photochromic lens that worked well. I own a pair of these and found them a very close match to the Alibi. The Alibi's lens is better in low light, while the Alleycat's lens better at shedding water droplets. The Melons are not only £60 less but you also get a hard case, which is disappointingly absent with the £200 Alibis.

But you don't need to spend that much for photochromic glasses. The Tifosi Slice Fototec Light costs just £94 and Stu also found they could be ridden into the night, though their lens coverage is limited.

For an even more budget option, Decathlon offers its VR Race II Photochromatic HD sunnies, which come in at very wallet-friendly £49.99.

Conclusion

Koo's striking-looking Alibis are a very good pair of sunnies. They have a top-quality photochromic lens that's suitable for the majority of year-round riding in the UK. I think they're probably best suited for smaller heads and it's a little tricky removing the lens, and while the price is undeniably expensive, it is comparable to other premium photochromic glasses.

Verdict

Top-notch photochromic lens that works extremely well in low-light conditions, with a quality befitting the price