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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 '13 at 22:16
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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 '13 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 '13 at 0:16
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Take it in your primary hand and hit another surface (try the soft ones first, as the palm of the other hand), preferably in the direction the batteries are oriented. Repeat with different strength. I found out that it's really easy to turn off cheap tail lights this way. Then experiment with spacers etc... –  Mladen Jablanović Dec 3 '13 at 12:58
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Are you using rechargables? If you are, they have a tendency to cut out in some lights without warning since the circuitry isn't designed for their voltage characteristics. (See: Texas Instruments Note SNVA533). You could check the soldering (with a loupe) as well outside the battery area and see if anythings a bit off. –  Batman Dec 5 '13 at 4:41

3 Answers 3

up vote 3 down vote accepted

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 '13 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!) –  Mσᶎ Dec 3 '13 at 1:28
    
+1 Good solid answer. –  andy256 Dec 3 '13 at 5:20

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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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.

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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 '13 at 23:05
    
While I ride with multiple lights from different manufacturers for safety reasons, without knowing the mode of failure I can't feel secure with multiple lights. Additionally "overseas" varies. The major competitor to Chinese battery lights, German hub driven lights, are also "overseas" and SON don't appear to be driving the Chinese out of the Australian market. –  Samuel Russell Dec 3 '13 at 0:06
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While your answer doesn't really answer the question so I can't upvote it, I agree that using multiple lights is a smart thing to do. Especially for the taillight since you can't easily see it so you may not notice that it turned off. Since I use NiMH rechargable batteries, there isn't much of a light dropoff when the batteries are discharged, the light seems fine one moment, then quickly dims and turns off. I try to replace them on a schedule that prevents them from discharging during my commute, but if I accidentally leave it on all day at work, the batteries might drain ahead of schedule. –  Johnny Dec 3 '13 at 0:15
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@Johnny I agree: I'd strongly suggest kiloseven find or ask a question on safe bicycle lighting and submit bits of this answer there. Its a good answer to a different question. –  Samuel Russell Dec 3 '13 at 0:18
    
@SamuelRussell - Agreed - redundancy in lighting doesn't seem to be covered by any existing questions, but can enhance safety. –  Johnny Dec 3 '13 at 0:23

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