What the Experts Say about Dynamos versus Battery Powered Lights

Here are some statements regarding low wattage and generator lights from bicycle advocacy organizations:

North Carolina Bicycle Coalition http://www.humantransport.org/bicycledriving/library/lights/lights.htm
...a cyclist operating at 15 mph can see well enough with less than 600 candlepower (e.g. 12 watt halogen), and a cyclist operating at 7.5 mph can see far enough in with less than 150 candlepower (e.g. 3 watt halogen). The light provided by a bicycle headlamp may be focused into a narrow beam for maximum range, or may be spread out for better peripheral vision. A three watt lamp can be focused into a beam suitable for high speed cycling on the darkest roads, but will not give much illumination of turns. North Carolina Bicycle Coalition

Sacramento Area Bicycle Advocates (http://www.sacbike.org/articles/article.php?mode=display&lognum=17)
"If you want to cycle at low speeds in areas with street lights, other ambient lighting, or when there's a full moon on a cloudless night, a low wattage light is OK. If you actually want to see obstacles in darker areas, you need a more powerful light, from 10 to 30 watts or more. With the added power come a couple of penalties, much higher costs and more weight. These lights can run from $70 to well over $200. Their weights, mostly from the batteries (often rechargeable NiCads) can go from 2 to 3 pounds."

Wikipedia http://en.wikipedia.org/wiki/Bicycle_lighting
"There are several types of bicycle lights available. In North America, most commuters choose to use high power halogen lights, which operate from a rechargeable battery. In parts of Europe, low power lights that operate from a dynamo are still popular, but are slowly being replaced by safer, higher power, battery operated halogen lights. Front LED lights are useful for being seen, but do not project a good beam for illuminating the road. For rear lights, LED flashers are popular in North America, but illegal in most other countries. A better choice for a rear lamp, where flashing lamps are legal, is a xenon strobe, because it is less directional.

Many cycle commuters build their own lighting systems with commonly available lamps, batteries, and chargers. One method is to use a generator stored in the hub of the front wheel. This method requires no external batteries or chargers because the power source is always available."

Bicycle Federation of Wisconsin (http://www.bfw.org/new_bfw/articles/brightideas.php?printable=true)
"Generators One of the oldest lighting systems is the generator. This type of lighting works off a generator (or dynamo) that is powered when it makes contact with the bicycle's tire. A generator system is often set up to power a headlight and a taillight. These systems are reliable, but often lack the power to really light up the road. Generators are more popular in Europe than in the United States."

Ken Kifer http://www.kenkifer.com/bikepages/traffic/traffic.htm
"For commuters, the best front light is the very bright rechargeable lamp. For the day tourer, it's important to carry a small, battery-powered lamp for the trip that ends up finishing after daylight has ended. Unfortunately, many of the lights sold for this purpose are inadequate. For long-distance travelers, those who ride long distances in the country at night, or those whose habits are sporadic, a generator front light is bright and always available for use."

Ice Bike (http://icebike.com/Equipment/lights.htm)
.....my personal first priority is brightness. Not just because its hard to see, but because being seen is even more difficult. If you are doing city riding, you need more light than country riding. 6 watts is adequate on a dark country road, but would be totally overpowered in a city environment.

Ken Kifer (http://www.kenkifer.com/bikepages/commute/accessor.htm)
I have been using generator lights for many years, and I find them very suitable for riding in the country at night and on touring trips. There are no batteries to fade or go bad, and the light gets brighter while going downhill. The beam is very wide and thus visible from all sides. On the other hand, a generator light is not very bright in city traffic and goes out each time you stop at a red light.

I have great respect for Ken Kifer's writings. He was able to admit that he used dynamo powered lights, explain what the advantages were to dynamo powered lights, while at the same time stating why what he used may not be be the right solution in other situations (in this case, city traffic).

Peter Cole
"I'm always surprised that so many serious cyclists who otherwise recognize the equivalence of bicycles to other vehicles take exception to lighting requirements. I wouldn't dare operate a motorcycle with a 3W light, so I don't understand the recommendation to operate a bicycle (at often similar speeds ) with such inadequate lights. Perhaps this was an accommodation to the technological limitations of the past, but in these times of readily available and relatively cheap, high-wattage alternatives, it seems a bad way to go."

Steven Goodridge ( http://www.humantransport.org/bicycledriving/library/lights/lights.htm)
"...a cyclist operating at 15 mph can see well enough with less than 600 candlepower (e.g. 12 Watt halogen), and a cyclist operating at 7.5 mph can see far enough in with less than 150 candlepower (e.g. 3 Watt halogen). The light provided by a bicycle headlamp may be focused into a narrow beam for maximum range, or may be spread out for better peripheral vision. A three Watt lamp can be focused into a beam suitable for high speed cycling on the darkest roads, but will not give much illumination of turns." This is a good, succinct, evaluation of the trade-offs inherent with low power lighting.

Paul Dorn (http://www.runmuki.com/commute/commuting10.html)
"The more expensive lights, which use a rechargeable battery mounted on the frame, are essential if you ride at night."

One incorrect statement, often promulgated by dynamo proponents, is that headlights intended for use with dynamos have superior optics than what are used in high power headlights used with battery powered systems. The compare the lowest quality battery powered lights against higher end dynamo headlights to reach this conclusion.

What’s the Bottom Line?
The most important thing is that cyclists that ride at night use adequate lighting. While the 12V/6W dynamos do produce adequate illumination, they are far too costly for most cyclists to consider. It would be a shame if the dynamo proponents convinced cyclists that they should not purchase low cost, high quality, battery powered lighting systems simply because these systems rely on mains power for recharging.

I am normally very much the purist, and try to be self-contained. I tour with panniers, carrying everything. I stay away from aluminum frame bicycles, non-lugged frames, and threadless headsets. For touring, I would normally not ride much at night, and would probably use a handlebar mount Mag Light for the times I would have to be out at night. If I were going on a long tour and expected to do extensive night riding then I would splurge and buy the 12 volt, 6 watt dynamo, because it would not be practical to charge batteries.

I wish that it were possible for inexpensive, dynamo powered lights to provide adequate illumination for commuting, but it isn't. I recognize that few people can afford nearly $400 for a 5W dynamo light.  For commuting, where there is no problem charging batteries every night, a high power quartz-halogen set-up is more economical.