BTwin VIOO 320 USB Dual Bike Light

The BTwin VIOO 320 Bicolour bike light is a reversible red/white LED with two modes. While I'm not totally convinced by BTwin's claims regarding visibility distances, at 22 and 7 lumens respectively, it's a surprisingly useful contingency light – the sort you might lend to a mate should one of their blinkies unexpectedly power down.

As the photos illustrate, it's a very compact design, although it occupies more handlebar space than some of the thimble-sized blinkies, such as the Lucas F-40 and similar. However, at £8.99, it's considerably cheaper.

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Despite this, materials and build quality seem reassuringly good. Inside that familiar rubberised monocoque shell cum strap (which is very secure, although benefits from some gentle pre-stretch before being mounted to beefy bars) sits a single diode, lithium-ion battery and switchgear.

The battery is designed to serve 500 charge cycles, so at a conservative estimate that's at least three years' hard use and the retail giant's standard two-year, no-quibble warranty adds further peace of mind.

A full mains charge takes just under two hours and the diode emits a subtle red pulse during this phase. Similarly, when reserves dwindle, it flashes intermittently, giving 28 minutes and a sporting chance of getting home before powering down.

There's no IPX rating, but so long as you've reinstated the USB port cover properly, there's little chance of water/similar ingress getting inside. Cursory blasts from the garden hose made no impression either.

The simple top-mounted switch is intuitive to use, requires a definite two-second prod, and is easily operable in middle-weight full-finger gloves. Ours defaulted to white steady, another prod engages flashing, and two further nudges selects the red beams.

LED technology is improving all the time in terms of output and efficiency. Curiously, despite the disparity in power, both flashing settings are reckoned to achieve 9 hours from a full charge. Calling their bluff, I'm pleased to report 8hrs 54mins and 8:56, which should be accurate enough for all but the most pedantic.

Performance/visibility

As I mentioned earlier, in both settings, it's quite a potent little light, especially relative to some household names costing twice as much. The highest, 22-lumen front flash isn't quite a daylight mode in the sense of being visible to other traffic on brighter days. However, it's surprisingly useful when skies are overcast, thanks to the combination of pace and pure white diode.

Past dusk, oncoming traffic seemed to register at around 300 metres, not quite the 450 metres quoted, even along otherwise deserted lanes with starry skies.

This also compensated for the lens's relatively small peripheral punch around town. Even in the latter context, paired with my Univega's potent Exposure Revo dynamo lamp, the BTwin registered first. Distance-wise, by my reckoning it's between 150 and 200 metres. Again, short of those cited on the packaging, but good nonetheless.

The steady mode is quite piercing and reckoned to project a pool of light to 11 metres (36ft in old money). It's not intended as a light in the legally accepted sense but passable for tackling roadside mechanicals, map reading, pannier foraging and similar close detail stuff. Visible to 450 metres? Not by my reckoning, although, with main systems switched off, a very reasonable 200m is nearer the mark, and that's along unlit roads on clear nights.

> Buyer's Guide: The best front lights for cycling

The red, or rear, setting is brighter than 7 lumens would suggest, and again BTwin cites 300 metres in constant and flashing. Fellow riders concurred with my estimate of 200m in flashing, less around town; on the flipside, it's less intense at close quarters than some, so passable for group riding, although my generally diplomatic persuasion erred towards the constant setting.

Used thus, visibility is around 80 metres, dipping to 40 in suburban/urban settings – a few split-second stealth moments when exiting roundabouts left me slightly uncomfortable, although the same could be said for other bijoux models in a comparable context.

> Buyer's Guide: The best rear lights

When all's said and done, this is still a very capable contingency system and deserves a place next to the patch kit in a wedge pack.

Verdict

Some doubts over the claimed visibility, but nonetheless an inexpensive and surprisingly bright contingency light