Originally Posted by
debit
Building a wheel can be expensive, yes. But if you compare the life of the hub to how much you'll have spent in batteries, the hub probably ends up being cheaper in the long run. Better for the environment too. And really, the quality and quantity of light from a dyno hub and some decent lights is better than any battery or rechargeable light I've ever had.
This is what I paid: Lights were from Peter White and I think front and back combined cost me maybe $60 with shipping. The wheel (hub, spokes and rim) was $132, so lets be generous and say it will cost about $200 to get set up. $200 would buy a lot of batteries, true. But I'm really happy with my set up and consider it money well spent.
Let's compare apples to apples and not cheese to chalk. A "quality" battery light system that has a comparable output to dynamo systems uses rechargeable batteries that will last a very long time (2 to 5 years) and not add that much cost to the system. In today's light market, $200 doesn't just buy a lot of batteries, it buys a lot of light. Current Magic Shine clones are going for $25 per lamp. Battery packs are going for around $10 so I could buy a battery pack every year for 20 years. The realistic operational life of a hub is much less than that.
Originally Posted by
vanttila
Directed at the OP, who said he knows "nothing" on the topic: From a quick googling I found that most dynohubs today draw 3 watts. If the OP pedals at 80 watts avg. during his summer trip, that's a bit under 4% of his power that goes into the light. That's not major, but worth noting. In addition, dynohubs weigh 1lbs and up, though the weight is at the center of the wheel, which lessens the power wasted in this (the rotational energy for a heavy wheel is higher, and it's all wasted when breaking, so lighter wheels are better). In addition, setting up a dynohub requires building a wheel around it (or buying one that comes with a wheel, I suppose), which may or may not be a problem depending on the OP's skills and budget. Dynohubs alone cost $100+.
Once you have the dyno set up, it's true that you have one less thing to worry about, and you "won't have to remove your light every other day to charge." Still, I'd recommend investing in a quality flashlight, handlebar mount, and a battery charger, with a couple of spare batteries. Buy them online from dinodirect, t mart, or another such place and you can get the whole deal for <$25. I ride home in the dark 5 times a week and only need to change the battery once a month if that.
Ah, the elephant in the dynamo hub room
It's also been called the "Free lunch gene". Dynamo hub people don't what to admit that you don't get something for nothing. Even when
not engaged, the hubs generate some drag and it increases with speed. When engaged, the drag is significant as shown in the article that pdlamb linked to. While it is true that "good" hubs have a low drag, the drag isn't zero. At 30 km/h (18mph), the drag is the equivalent of adding a kilogram to the mass of the rider/bike. Turn the light on and that jumps to 8 to 10 W of drag according the the Bicycle Quarterly article which is the equivalent of a adding 4 kg to the bike and rider. I would suspect that the drag is independent of the rider weight so the impact on a smaller rider would a much higher percentage of the rider's power output. Another way of looking at it is that the drag will require the rider to input more effort to maintain the same speed.
Battery systems add a tiny bit of aerodynamic drag...you don't get something for nothin'
...but the drag will be tiny comparably.
Watts are a measure of power consumption, not of light output. Using watts to compare light output works only in an apples to apples situation.
If you're using watts to refer to light output, then I'm guessing you're using incandescents of some sort? (Halogens are also incandescent.) Remember that incandesents are very, very, inefficient. It helps to think of them as heaters that give off light as a waste product. Most of the power consumption goes into heating the filament, in much the same way as tube amps use most of their power to heat the tubes.
My first real light was a 10-watt NiteRider TrailRat halogen. Its light output was roughly equivalent to the pair of 200-lumen DiNotte 200-L-AA lights I replaced it with. They draw less than three watts each.
The current crop of LEDs are very efficient. Both my dynamo lights are easily 2x to 3x brighter than that pair of 200-lumen DiNottes, so, their 2.4 watts of power consumption is producing light output easily in excess of a 10 watt halogen--at least judging by my old eyes and memory.
The German lights all rate their output in lux, which is a measure of how much light actually falls on a specific target at a specific distance. It's a much better comparison than lumens, which is a raw measure of light output, not necessarily what ends up on the road.
Same goes for taillights, BTW. The pair of LEDs in my B&M Toplight Line Brake Plus draw a half-watt together, but are easily visible in daytime. This past summer I chased a bike on a sunny day to find out what taillight he was using in the daytime--a B&M Toplight Line Brake Plus. That's why I bought one.
While I agree that light output should be in lumens or lux (only if the distance to the target is specified), with a dynamo system does have a wattage impact on the rider. A battery system does not.