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I've had consumer battery powered LED bicycle lights fail mid ride without the battery being at fault. This has been spread across brands, weather conditions, ride lengths. The most recent failure is a rear blinkie that dies on a 6km commute.

Factors I've tested:

  • Water proofing. This causes one light to fail and later recover. But not the other which is adequately sealed.
  • Battery contact patches / corrosion. This caused a third light to fail intermittantly, but isn't present in the currently failing light.
  • Shock. I can't produce a shock that causes the blinkie to turn itself off.
  • Battery life. I've put it on to test if it fades over half an hour. It doesn't.

Help.

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    Cheap lights? I've never had an LED fail mid-ride except when caused by drained batteries.
    – Carey Gregory
    Dec 2, 2013 at 22:16
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    Ride with two, because with something so useful in maintaining metabolic integrity, redundancy is your friend. If it fails, take it back to the store. Overseas manufacturing drives everyone else out of the market, so if you go to a local electronics shop to make one for you with highest quality components, you end up paying through the nose for something which looks like it was homebuilt.
    – K7AAY
    Dec 2, 2013 at 22:59
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    Yeah, when I used to ride at night I always carried a backup clamp-on handlebar light. The battery can die unexpectedly, the lamp can burn out (though not as much now with LEDs), or a connection can go bad. In one case the bracket holding the light simply broke off -- on the first day of a 4-day ride.
    – Daniel R Hicks
    Dec 2, 2013 at 23:05
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    I've never had a quality bike light turn off in mid-ride (except for the one that fell off when the rackmount bracket broke). However, I have had several dog blinkies turn off due to shock. The light would turn off when the dog shook her body to shake off the rain -- I couldn't apply enough force by shaking it myself it to make it turn off, but finally reproduced it by dropping it to the carpeted floor a few times. The problem seems to be a faulty switch or contact - maybe the batteries temporarily lose contact during heavy shock (which in your case could be due to your bike hitting a bump).
    – Johnny
    Dec 3, 2013 at 0:10
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    I'll try some more advanced shock testing if you've got some advice on how to replicate intense shocks?
    – Samuel Russell
    Dec 3, 2013 at 0:16

6 Answers 6

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In my experience cheap lights die, and some more expensive designs are prone to failure. Bike shops sell cheap lights because that's all some people will buy, and better they have a dodgy light than no light (there are enough cyclists without lights already).

All the factors you list come down to one or two factors, depending on whether you consider "built to an excessively low price point" to be a factor. The other is poor design. It's not easy to make a bike light that works, and doing so costs money. If you search for bike lights on kickstarter those projects often document the design and testing (which is one of the few places you can read about it).

I've had lights intermittently turn themselves off while riding, and that's either something hitting the on-off button or the batteries momentarily disconnecting when bumped. Rather than reproduce the latter I prefer to add conductive spacers with the batteries and see whether that solves the problem - add a chunk cut from a tin can or 5-10 thicknesses of aluminium foil at one end of each battery.

I expect to pay ~$40-$60 in Sydney for a decent rear light, maybe $30 online, and if they don't last at least a year I take them back. And I do take them back. Maybe 5% fail within a month. For front lights I pay the same as a rear one for a blinky, ~$100 for a "to see by" light. But I also DIY and use dyno lights (more expensive up front, heavier, but cheaper in the long term).

This is easier if you're running multiple bikes, whether for yourself, your household, or your group of friends. Or you have a decent LBS. Buy 2-3 different lights to test, pick the one you all like the most and buy one (or more ) each, plus a couple of spares. That way you know you're getting something that works, and have a communal spares pool. You can get a similar effect by buying what everyone else has. But buy exactly what they have, a lot of bike lights look very similar and a cheap clone is not the same as the real thing.

I have lights regularly last until the LEDs are so dim the light is worthless. Specifically, I have a box full of "bike lights and bits" in the garage that contains 5-10 rear lights and 3-4 front ones, none of which I would use today as my primary light (I use them on trailers and take them to group rides to lower the suicide rate). The front ones I expecte to fail, white LEDs have a finite, short life that in a "every weekday in the winter" light means 2-3 years. Rear ones mostly just fall to the progression in LED efficiency, in that "the same" light bought next year will be noticeably brighter (front ones too, obviously).

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  • Thanks Moz. I just tested "gapping" the batteries by pushing down the springs while the light was on, and the blinkie failed to restart. That's a good proxy for an extreme shock and I'll try adding some conductive spacers to get a tighter fit. I agree entirely regarding blinkies and I tend to treat them as disposable parts. I guess it is now time to add the rear dynamo light to my bike.
    – Samuel Russell
    Dec 3, 2013 at 1:15
  • If you can, then yes. The latest front lights from BM are also pretty spiffy (I just upgraded my 10 year old light to a Lumotec Eyc and WOW!)
    – Móż
    Dec 3, 2013 at 1:28
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If I put my main rear light on my wife's road bike, on the pannier rack, it will switch itself off. On my hybrid on the same potholed commute it doesn't. Unless I ride straight off a kerb, when it might. That sounds like shock to me given the difference in tyres (100psi 700x23, 65psi 700x35) and the subjective feel of the ride.

I've had a little blinky die from water ingress, but that was pretty much a bow wave from my front wheel. Dried out it kind of works but the switch is corroded an unreliable.

So I strongly suspect shock on the battery terminals in your case - maybe the frequency of the bouncing affects it. Perhaps repeating the ride with the terminals taped or wedged to the battery might answer it.

A further suggestion though - if the batteries are on the way out, it's possible that the higher internal resistance on a cold ride would cause them to drop in voltage quicker than indoors, and possibly cause the light to cut out. But I wouldn't expect this to be an issue in blinkies, only in something designed to use rechargeable batteries. If your ride was cold, perhaps try leaving it on in the fridge or even freezer for an experiment.

In terms of solutions: multiple rear lights are the way to go - they help define your size as well as giving redundancy. I'm now up to 2 steady on the bike, plus a rather weak flashing one in the saddle, then a flashing rear light modded into the battery box of a head torch on my helmet.

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I agree with Jablanovic about striking the lights in the direction of the batteries' orientation to test them. I have two blinkies with this problem. Folded aluminum helped but didn't fix it. Then used narrow strips of duct tape parallel to the batteries to hold them in place. That completely fixed one and only helped the other. For that I put a 50uf (micro farad) dielectric capacitor in parallel with both batteries. Didn't need to solder, just wedged the leads behind the containment plates. Make sure the batteries' polarity matches the capacitor's.

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    What does the capacitor do in this case? There doesn't seem to be any need to smooth the output of the battery or suppress RF, so isn't it just more spacer like the foil?
    – Móż
    Jan 25, 2016 at 8:28
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    A capacitor can supply current to the light during the short break when the batterey is disconnected. Please keep in mind that a cap - depending on its value - can only deliver the current for a very short moment. This is easier for a rear light with a rather low current need, that for a front light, which needs more juice.
    – corvairjo
    Jan 25, 2016 at 13:45
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Answer: Bad luck.

I would contest the idea that consumer battery powered led lights generally fail mid ride, you have just had bad luck or been buying bad lights.

I have only replaced one rear light on one bike in 5 years, this replacement was necessary because I came off the bike on an unexpected icy patch on a switchback in the woods... the light still worked but the casing was shattered.

I have four front lights which all still work, the oldest is 7 years old.

All of the lights, even the expensive ones, are made in China (note: the expensive ones actually see the least use since I only put them on for night riding in the woods, while the cheap lights are on my bikes almost all the time.)

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How about getting a light with a position switch rather than a push to on/off type? At least in the position switch type when the batteries got disconnected in a shock and recovered shortly, the light will still be on since the switch is still in the on position.

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    It's a nice idea but have you seen one in the last few years? The only one I've seen was dreadful; a good shake was enough to make the switch slide.
    – Chris H
    May 31, 2016 at 15:50
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The flat battery that was not able to power the light any longer may suddenly work again if turned on after some time. Hence even if you say "battery is not the reason", my own experience strongly suggests it still may be.

The only trustworthy level on my own light is "fully charged", with everything else going through in fifteen minutes. Hence if something less is shown, charge before you ride, carry the spare or even both.

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