Dynamo bike lights – do they vary in power draw and drag?

[Samuel D]

Use batteries.
No drag at all other than aerodynamics.

You’d think from the way I go on about drag that that would be the best idea. But I am completely enchanted by the idea of never having to worry about sunset or keeping batteries charged. (I also have dreams of riding straight through the night on occasion, though I’ve never actually done that before.)

There is also a near-total shortage of battery lights that are lightweight, long-running, have good beam shapes, are simply and elegantly designed with metal housings, and are halfway affordable. There is even a mounting problem, with nearly all of them clumsily mounted on the handlebar rather than at the fork.

[FarOeuf]

borrow a front wheel with a dynamo hub? I run a SON Delux and Supernova E3 Pro 2, and I can't tell any difference between it and a normal hub. I never turn it off, and I'm currently doing 300-400km rides. Fine to muse over the physics of it all, but you really think it makes any difference? Or any practical difference after the road surface, tyres, body state, traffic, humidity, wind drag, etc, etc have all added their effect.

I'm assuming you're not selecting a dynamo hub for track racing?? maybe you could add a dynamo and offset the drag with a full aero helmet and skin suit?


EDIT: the best thing I ever did was get a dynamo hub and decent headlight. I now love riding through the night, it's opened up a whole new area of riding.

[Merry_Wanderer]

I'd echo Faroeuf's suggestion, see if you can borrow a dynamo wheel. My dynamo lights have transformed my cycling, I now commute all year round, whatever the weather, whatever time I start or finish work and I look forward to doing longer audax events involving riding at night

[PH]

EDIT: the best thing I ever did was get a dynamo hub and decent headlight. I now love riding through the night, it's opened up a whole new area of riding.

Exactly that and what Merry_Wanderer said. For anyone who considers a bike to be transport rather than just leisure, having lights fitted, available and ready at all times just makes sense.

[interestedcp]

The Philips is positively reviewed here. It’s also €66 in France and has a metal housing. Although it’s big, it has an attractive shape with simple geometric forms (as does the smaller Edelux). I much prefer this clean style of design to the swoopy Busch & Müller style. In fact, if the B&M lights weren’t so ugly I’d likely consider nothing else!

I would take that review with a spoonful of salt. I find his reviews somewhat cranky and idiosyncratic. It is not so much that he is highly opinionated about certain things like LED artifacts or beam shapes, but that he confuses these subjective opinions with objective facts. He also have a direct economic interest in what he reviews since he has a webshop too that sells some of the reviewed items.

Anyway, despite that the Philips Saferide by all accounts is a good light, it is simply outclassed by the new 80 Lux lights both in light output and beam shape. I see no reason at all to buy it at higher price than the IQ Cyo Premium.

Another point worth remembering is that what really matters aesthetically is how the lights look on the bike. B&M Cyo's tend to look good on bikes, and the design looks much better in real life than on photos.

Can’t find an ‘IQ2’ version of this. Is that its official model name? B&M’s range of models is really hard to understand.

Ups, typo. IQ2 is the Luxos, not the Cyo.

But if you or others would like to recommend me a light, these are my preferences in rough order of importance:

[snip]
That list pretty much describe the SON Edelux II or the IQ-X, except for the bit about low cost.

If cost in an issue, then the simple IQ Cyo Premium has the best cost/performance value.

Some word on the differences between the IQ Cyo and the Edelux II. Besides better cooling and and RF shielding, the Edelux II also have a scratch resistant optically treated glass lens. The switch is a magnetically operated Reed switch which is a very reliable switch type that doesn't wear out and is very resistant to corrosion too.

They also differ in waterproof design; the Edelux II has encapsulated electronics and is a sealed unit with two o-rings.
The Cyo is semi-open and even have a "drainage hole" in the bottom (protected by a labyrinth). The reason behind this design is AFAIK is to prevent condensation to form inside the housing, something that can be a big problem for bikes since they can be ridden in freezing weather but stored inside in a warm house. By letting the condensation escape easily, the Cyo avoid slow corrosion of the electronics inside.

In practice the Cyo is extremely water resistant, but if long distance riding in heavy rain is something that you do occasionally, or if you ride without front fenders, then the fully encapsulated Edelux II is a probably a somewhat better choice.

[PH]

Plenty of talk about the Edelux II, it's worth remembering that the original is still an excellent light and are being heavily discounted. For example £80 from SJS
http://www.sjscycles.co.uk/schmidt-edel ... prod26574/

I've ridden alongside someone with a II and compared it to my original, there's no doubt it is a better light, wider beam and a bit brighter, but not enough to stop me being very happy with mine. if I was buying now I'd still be tempted to save some money and get the original.

[edocaster]

I'm guessing that dimmer lights don't cause less drag, if comparing lights which adhere to the prevailing (German) standard. The reason is the lights are designed to top out at 6V, taking whatever current comes out of dynamo (which is usually less than 600mA) minus whatever a rear light may take.

The dimmer lights may simply waste power with older LEDs (or even incandescent bulbs), hobbled optics or even just diodes or resistors to trim off some power.

This isn't my experience. When I ran a 1 watt B&M Fly of a Lightspin bottle dynamo, it never slipped in the wet. But when I changed it for a B&M Cyo, it did unfortunately slip in the wet. The Cyo has a more powerful LED (not sure how much), hence the resistence at the tyre.

That surprises me a little. Is the Fly really a 1 watt light?

My experience with the Axa Pico 30 is it will light at 3 to 4V (flickering on a hub dynamo), but the voltage will rise with speed to about 6.2V. Current I'm guessing will stabilise at 500-600mA. So it will draw 3W, but possibly rising smoothly to that point.

Perhaps a more powerful light won't light at all at 3 to 4V, but only comes on at 6V. The sudden jump in power consumption may explain slipping bottle dynamos.

Maybe I'm wrong about this, but to stabilise at 6V I assumed all 3W dynamos needed 3W lights. If there was a way to stabilise at 6V without taking the full current of the dynamo, that would make products like 1.5W dynamos somewhat pointless.

[Brucey]

most LED lights are quite unlike tungsten bulbs as loads. The forward conduction characteristic of the LED itself can dominate this. Many of them don't draw much current below ~4V (hence the flickering at low speeds) and thereafter they will take whatever current the generator can dish out, more or less.

The LED itself will normally have a gently sloping characteristic so might drop ~5V @ 600mA, so add in a little rectification and you get about 6V total. Low power lights may be regulated such that excess current is wasted in a parallel shunt, thus protecting the LED. This means you can often end up with the same power and drag in the generator with a 'low power light' as with a high power one.

If you try to draw less current from the generator the voltage rises. The way this occurs varies strongly with the generator type (by contrast using the generator as a current source is far more predictable). But if you want the highest efficiency (i.e. most power total or most power per unit drag at speed) then matching a higher impedance load to a given generator is probably the way to do it.

A crude way of doing this at speed is simply to run two LED lamps in series . With clever electronics you can make the lamps switch between parallel (low speed) and series (high speed) operation but you can do the same thing with a switch and nothing will blow up.

cheers

[Samuel D]

I would take that review with a spoonful of salt. I find his reviews somewhat cranky and idiosyncratic.

He’s certainly cranky, but I find his reviews useful if not necessarily the last word. At times it almost seems he has a slight anti-German bias (SON) or pro-Dutch bias (Philips), which may be colouring his views.

Anyway, my chief interest in the Philips was the light colour. I am starting to think that that is not worth so much after all and that the Philips is also a bit too bulky for a sleek bicycle.

Another point worth remembering is that what really matters aesthetically is how the lights look on the bike. B&M Cyo's tend to look good on bikes, and the design looks much better in real life than on photos.

Interesting observation. I wish I had a chance to see these lights lined up in a row in a bike shop.

Do we have any opinions on the Busch & Müller LUMOTEC IQ2 Eyc N plus (what a name!) if I decide I should spend less? It’s much smaller than a Cyo, but small is typically worse when it comes to optics of all sorts.

[tatanab]

Anyway, my chief interest in the Philips was the light colour. I am starting to think that that is not worth so much after all and that the Philips is also a bit too bulky for a sleek bicycle.

The Philips BATTERY light (80 Lux) is bulky and heavy, the dynamo light (60 Lux) is a lot smaller so make sure you are looking at the right light. I have both. I used the battery version some years ago, the beam is bright and wide on the dim setting such that I seldom used the bright setting even for riding in pitch black lanes. I've been using the dynamo version for 3 or maybe 4 years now. The beam is quite bright enough but not as wide as the battery light. I have had no problems, but know people who have sent them back because they did not work or did so only for a short time. It seems Philips had quality problems which is perhaps why they have dropped out of the market. Given that, I do not think I would recommend them. Fortunately mine, being old ones, have been reliable.

[MikeF]

I have a Philips 60 lux light (2 actually bought from Amazon for just under £30 each) and also a Luxos B. The Philips is certainly not outclassed by the Luxos B; they are roughly the same, but I prefer the Philips.

One weakness supposedly of the Philips is the mounting bracket, but I have removed that and mounted the light on the narrower part of the handlebars using a bracket from SJS and a longer bolt. Also fork mounted lights can get very dirty.

I also have a Cyo but not the 80Lux version. Not a bad light and the standby capacitor seems to retain its charge for weeks!

The largest amount of energy in cycling is combating air resistance; I'm not sure that you travel quite as fast in the dark as in the light, because of visibility and would therefore save a few watts that way. But then, of course, you may.

[[XAP]Bob]

CJ calculated the drag on a SON to be equivalent to climbing one foot per mile.

I take your point, but that calculation (here if that PDF downloads) was for the lights-off drag of the best hub on the market and a heavier cyclist than me.

As reported there, even the lights-on drag is low. However, I think I would at least sporadically feel a difference of 6 W. More importantly, whether I feel it or not, it exists. Even 2 W, if there is that kind of variation between lights, would matter to me.

Good thing you keep tyre pressures within 2% of the ideal, changing them when you stop to wee...

[edocaster]

This means you can often end up with the same power and drag in the generator with a 'low power light' as with a high power one.

If you try to draw less current from the generator the voltage rises.

Exactly. So, in other words, if you want to keep things at 6V (as all the German legal lights are supposed to), using a (German-)standard dynamo, your load will have to suck up about 3W at speed. The only way to lessen this, while still keeping voltage clamped, is by finding a light that stays below 6V. But such a light would generally not adhere to standards (as it might not safely co-exist with a 6V rear light).

[rofan]

As an addition
BUMM offers now the LUMOTEC IQ Onefive for the "new" Shimano 1,5W Dynohubs with ( just) 30 Lux.
(New calculations for the drag

[Steveo2020]

Hi

I have a Shimano generator - can't remember the model but one of the better ones. I love it, and wouldn't go back to battery lights. However, I do notice the vibration when the lights are on. It is subtle but not hard to detect. It's the kind of thing that might drive you nuts if you were very tired...

I am just building up a bike with a Sturmey Archer generator (x-fdd) and I will be interested to see if I get the same effect (the same bike used to have the Shimano generator on it).

Cheers

Steve