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Both on this site and "in real life", battery-powered lights appear to be at least as popular as generator-powered lights.

I have always been slightly confused by this. To me, a generator-powered light seems the better solution if you need light regularly, because there's no need to worry about charging, and because they can be permanently attached. Yet many people seem to not only prefer battery-powered lights, they appear to not even consider a generator.

Why is that so? What are the advantages to battery-powered lights?

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8 Answers 8

up vote 12 down vote accepted

The main advantage, in my view, is that you can more easily add/remove battery-powered lights.

Why this may be desirable:

  • Theft resilience. I take my lights off the bike and carry them with me if I'm parking my bike outdoors for longer than a few minutes. Caveats: This can be more of a downside than a benefit, depending on your situation. (I can't imagine a thief taking the time to steal a generator-powered light, but I'm sure it happens sometimes.)

  • Flexibility. I don't bother to take my lights with me unless I know I'm possibly going to need them. If I used a generator-powered light, I would be pretty much stuck with it all the time, even if I'm only going to ride during the day. Caveats: This is, however, not much of a positive thing, unless the lights you use are particularly heavy, or you happen to be a "weight weenie".

  • Interchangeability. I can swap my lights between my bikes very easily. Most decent battery-powered lights have an adjustable removable clamp that you can use to attach the light to any style of handlebar/seat post/other tube that you could possibly want. This means that I only need one set of lights that I can use between all of my bikes. Caveats: If you don't like to spend an extra 5 minutes swapping your lights every time you want to ride a different bike, this is not a plus.

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Actually, point one and two sound more like disadvantages to me :-). The interchangeability is a good one though; I didn't think of people with more than one bike. – sleske Feb 16 '11 at 17:15
@sleske Yeah, hence the Caveats :). It depends on how you want to use your bikes/lights. I can see why some people would prefer to have a permanent system that is always available. – Jason Plank Feb 16 '11 at 17:33
Hmm...I thought that one and two are advantages. It's pretty common for components to get stripped off of parked bikes. For example, at one point I had a seat stolen, which convinced me to remove it when parking. And, for 2, modern battery powered lights are easy to remove and fit in my pocket or pack. – user313 Feb 16 '11 at 17:45
I actually have 2 sets of lights for 3 bikes - all the bikes have mounts for the lights installed, so depending on what I'm riding that day, I can just toss the lights on that bike. No need to readjust the mounts. – zigdon Feb 16 '11 at 21:47

Cheaper, easy to fit, more widely available - and don't take any effort!

Probably most people's memory is of the side wheel dynamo systems when they were a kid that wore away tires, put out a feeble light and turned off when you stopped.

enter image description here

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I don't think they are cheaper, at least not the decent ones (though there may be more extremely cheap battery lights). "Easier to fit" is indeed true. – sleske Feb 16 '11 at 17:20
And congrats about the picture. It very effectively stirs up bad memories of creaky side wheel dynamo systems with me... (though, to be fair, there actually are decent side wheel dynamos now, which rarely slip). – sleske Feb 16 '11 at 17:22
A 4*AAA LED front light for $15 is tiny and pretty bright. Rear flashing red LEDs from a dollar store are good enough for most people. – mgb Feb 16 '11 at 19:02
all that needs to be said about Tire driven dynamos: – mcgyver5 Apr 27 '11 at 15:10

Battery powered lights are popular because of up-front costs and convenience. Also, the battery powered lights go with me between bikes.

These days one can get a set of bright, long-lasting, front-and-back, multi-attachable, battery powered lights for less than $30 (roughly 22.2 euros). And, that suits the typical recreational rider and probably most commuters.

A dynamo, means the most difficult is re-building a wheel; but easier is mounting a frame mounted wheel powered dynamo correctly...not to mention effectively wiring the bike. Many bike riders just don't want to deal with it.

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The cost is I think the main one. It's why I have one dyno hub between five-ish bikes. Also, I haven't seen a superflash rear dyno light, so even on my dyno bike I still use a superflash light on my helmet. Battery life is also now so long as to be ridiculous. With low self discharge rechargeables it's "recharge when you get around to it" territory - 100 hours of use or more. – Мסž Feb 16 '11 at 22:53
I've not gotten a dynamo-hub-powered light for the simple reason that it's be awkward and expensive to fit it up to a helmet light, my preferred style of headlight since I have four bikes I switch between. Four dynamo hubs and I'd have to be wired to the bike? Nope, not for me. If I only had one bike and I had lights on the handlebar, then I'd only be concerned with the cost. – Neil Fein Feb 22 '11 at 7:43

Tyre driven dynamos can slip in rain or sleet. Hub dynamos can't slip, but do have a tiny amount of drag even when turned off. For a commuting bike, it's not enough to worry about, but on a high performance bike that you hardly ever use in the dark, with battery lights you don't have any drag from something you aren't using (and can leave them at home if you know you wan't need them). And you can get battery powered lights that are much more powerful than dynamo lights. You can always buy a bigger battery, but there's a limit to how much power you can get from a dynamo. (On the other hand, no battery will last forever, and dynamo lights never need charging.) Modern LED dynamo lights are really very efficient, but for some off road use, many people want more (and dynamo hubs aren't really designed for that sort of use).

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ROI for dynamo lights is poor in the era of LEDs for the bulk of the population (there are always exceptions of course). I can buy a nice set of LED front/rear lights for around $50. Add-on regular batteries for another $5 or so. OK, I'm in for under $60.

I researched dynamos and I was looking at $250+ for just the power unit itself. Add-in another $50 of lights and I'm at $300.

I can buy 50 sets of batteries (we'll keep it simple and assume my savings will match inflation) for the upcharge of a dynamo. These batteries last years of usage with LEDs. I'd never even break even with a dynamo in my lifetime, nevermind actually saving money.

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Good point. However, this ignores the fact that dynamo lighting may require less maintenance, because there's no need to change batteries, ever, thus no risk of a battery going flat at an inconvenient moment. Whether or not this is a problem depends on how and when the bike is used. – sleske Jan 28 at 15:15
Also, you can get a dynamo for way less than $250. A decent side wheel dynamo is around $20-$30, a dynamos are around $50-$250, plus new wheel (prices from Germany, in US $). – sleske Jan 28 at 15:18
I left out maintenance because it's not a big deal either way. A spare pack of batteries (which can last a decade in such condition) with your spare tube/inflator is how you handle the battery powered lights. The dynamo requires periodic maintenance as well (cleaning/greasing) that you'll do at intervals based on condition. – Brian Knoblauch Jan 28 at 15:19
That's the point - with a reliable commuter bike, you don't necessarily need spare tube and inflator (at least I don't need them), so having to carry a spare battery pack is an extra nuisance. And I have used dynamos (both hub and side wheel) for years and never needed to clean/grease them. – sleske Jan 28 at 15:21

As mountain biking specifically doesn't seem to have been addressed in above answers.

  • Weight - who wants half a killo more when climbing a steep hill?

  • Wear and tear - while both quality battery lights and quality dynamo lights are expensive, the latter will need to be replaced more often, due to the dynamo hub wearing out, after the bearings fill with water and sand (after the third mudride).

  • Availability - dynamo hubs are actually not produced for mountain bikes at all (good luck finding through-axle dynamo hub).

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Why does a mountain bike need a through-axle? Can't you just use a hub dynamo with a solid (but robust) axle? – sleske Jan 28 at 15:28
@sleske, I can't really reply to that, apart form through-axles being more trendy, because of their (perceived) rigidity for the same light weight. – Vorac Jan 28 at 15:58

The main point of failure, and in my opinion the largest disadvantage of dynamo vs battery lights, shared by both hub dynamos and side wheel dynamos is: wiring.

The wiring on a bicycle is often very fragile, and in my experience it is always the first thing to break on any bike. This is especially true if you park in a bicycle parking area where your bike is subject to other bikes falling over or otherwise being mishandled by other people. Add corrosion of the connectors in wintertime (salty spray from the wheels) to this mix, and you understand why dynamo lights are not reliable. The frequent movement due to steering of the wire as it crosses from the front fork to the frame can also be a frustrating point of (intermittent) failure, that can be especially hard to find.

The rear wiring is especially vulnerable due to the length of the wire to the rear light (in case of a front dynamo, which is most common here) and the messy wiring that goes with connecting the light across the frame and rear mudguard. Some bikes use the frame as a conduction path (grounded frame) which at least eliminates one wire. This however requires conducting mudguards for rear lights and has the disadvantage that corrosion of the connecting points is common and leads to a gradual decrease in light output. The connection between a rear light and the metal mudguard is a notorious example of this. This also explains why bikes with a front side wheel dynamo and dynamo powered front light, combined with a battery powered LED rear light were very popular (in Europe at least) until a few years ago. This setup at least removes some of the major concerns (no more wire breaking due to steering, fewer connections and fewer and shorter wires)

There have been a few improvements in making more reliable wiring, such as integrating conducting strips into the mudguards and using semi-automotive type connectors that should make the wiring more reliable.

I would prefer to use dynamo powered lights on my bike, as I tend to forget my LED lights when I need them or forget to charge them, but the poor reliability of the dynamo/wiring combination prevents this.

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My experience is that with a good dynamo and lights, and with proper wiring (good wire, proper connectors [implying lights that have connectors] and careful fastening of the wire to the frame), a dynamo system can be quite reliable. My bike is constantly in the rain and parked and handled a lot, and I rarely have connection problems (maybe once a year). But of course this may depend on the specific situation. The wiring is certainly an added risk compared to battery-powered lights. – sleske Jan 29 at 9:23

Uh... Surprised why nobody's mentioned: 1) A dynamo-powered light changes intensity depending on speed (may not be an issue with modern LEDs which require low power); 2) No lights at all if you're stationary. This a serious disadvantage. If you have to stop in a dark area for whatever reason (puncture, something fell off the rear carrier), being seen is vital.

For me (2) is sufficient to never consider a dynamo. As far as the relying on batteries go, I have multiple lights anyway; it's unlikely that batteries will go dead on all of them at once.

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Well, not really. 1) is true, but with a proper dynamo 15km/h is enough for nearly full power (German standard TA 24 mandates 5.7V-7.5V from 15 to 30km/h). In practice, brightness stays constant once you reach 12-15 km/h with halogen, or 8-10 km/h with LED. 2) used to be true, but almost all modern lights for use with a dynamo feature a "standlight", where a capacitor is charged during use, which can then supply power for some minutes even at slightly reduced brightness. – sleske May 12 at 21:10

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