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I’ve never had a problem finding adequate taillights for my bicycles, but until recent years most bicycle headlights were dim. Bright ones were expensive, and required a large battery for power. A small, battery-powered headlight would alert other road users to my presence and was OK for riding under streetlights, but wasn't much use on a dark road or path. When touring, I’d use generator lights. With dark-adapted eyes, I could putter along without hitting too many potholes.
Since 2010, more or less, the efficiency of white light-emitting diodes (LEDs) has increased by leaps and bounds. Generators and rechargeable batteries have improved too. A compact, lightweight bicycle headlight can produce a beam rivaling that from an automotive headlight -- but there is a problem.
A common American folly is that More is always Better. The mid-twentieth century had its horsepower race -- every year, cars with bigger and bigger gas-guzzling engines. Bicycling isn't much for horsepower, but it still suffers from the More Is Better syndrome -- in a lighting race.
If a headlight is bright enough to light up the road, it is also bright enough to dazzle and blind people.
A typical bare LED, or one with a conventional mirror housing like a flashlight's, casts a circular spot of light. If aimed down at the road, a round beam is unnecessarily bright up close, making it harder to see more distant objects. If aimed high so brightness tapers off closer to the bicycle for even illumination, then the brightest part of the beam glares into the eyes of people ahead and washes out the view of the road in rain, snow or fog.
As LEDs improve, headlights are often promoted with lumen or candlepower ratings -- total light output, no matter where the light goes, and often, it glares into the eyes of oncoming road and trail users.
Certainly, for off-road riding, you want to see the overhanging tree branch which could smack you on the head. But on roads and paths shared with other users, a flat-topped shaped beam pattern like a car headlight’s avoids blinding people and puts more light on the riding surface. Tapering off the brightness toward the bottom of the pattern illuminates the riding surface evenly, far and near.
| Round beam pattern | Shaped beam pattern |
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The USA has no Federal standard requiring a bicycle headlight to have a shaped beam pattern. German standards, on the other hand, have led to production of the world's best bicycle headlights. 
Several high-performance European bicycle lighting systems with shaped beams, from Schmidt and Busch & Müller, are on sale in the USA. Asian competitors including Dosun, S-Sun and Shutter Precision have also entered the market. Schmidt, Shimano, Shutter Precision and Sturmey-Archer make hub generators which power some of these lights. Others are powered by lightweight, internal rechargeable batteries.
Most LED headlights with a shaped beam pattern, like the one in the photo at the left, can be identified by the scoop-shaped internal mirror, curving down from the top rear to the bottom front, with the LED hidden up at the top rear. You can also quickly identify the beam pattern by shining the light at a wall.
Hub-generator-powered systems are best for touring where you can't charge a battery, but rechargeable battery-powered lights suitable for commuting are more affordable. The photo at the left is of the Busch and Müller Ixon CoreIQ2 battery-powered headlight, $81 (as of October, 2015) at Harris Cyclery. I'm using a Taiwan-made DoSun light with a built-in battery; it costs $70 and serves me well. There is a smaller model which costs only about $40.
Adapters are available to convert the alternating current from a generator to the standard USB direct current, to power a cell phone or GPS device directly, or to charge a battery -- useful for evening lighting for a bicycle tourist. Many battery-powered LED headlights can be charged by a generator with an adapter, and also have a USB output, to serve as an external battery for other devices.
The better, newer shaped-beam headights make use of the brighter LEDs to provide a broader beam, most useful when there is a turn ahead. Many of the generator lights also have a "standlight" function: they store enough power to shine at lower brightness for a few minutes when the bicycle is stopped.
Many battery-powered LED headlights offer more than one brightness level. Highest brightness is needed only for fast downhill riding; lower brightness extends battery life under less demanding conditions.
A hub generator produces alternating current, whose pulses depend on the speed the wheel is turning, and so a light powered by a hub generator will flicker at low riding speeds. This is actually an advantage, because the peak power of each pulse allows the light to shine even though the average power would be too low. This flickering is not the same as the flashing mode with many battery headlights. That deserves further discussion...
Many battery-powered headlights flash. Flashing is promoted as attracting more attention, and it increases battery life because the light is only on for a fraction of each second. But -- a flashing headlight is of little use to light a bicyclist's way, is hard to track, and can trigger seizure disorders in people who are prone to them.
It's especially annoying when a headlight glares into people's eyes and also flashes. Cyclist Joshua Putnam, who lives near Seattle, Washington, describes how these problems play out:
Bicycling east on the I-90 bridge in the dark, watching two faster riders who'd just passed me, pulling away from me up the bridge.
A westbound rider comes around the corner with the most dazzling flashing headlight I've ever seen.
Ahead of me, the lead rider, blinded by the glare, slows down. The second rider doesn't see the first rider has slowed down, and veers left to avoid a collision.
As the westbound rider squeezes through, he screams "@$$#01&!" at the second rider who had veered into his path.
I stop and protect my vision with my helmet visor as the westbound rider continues blindingly down the bridge.
Thoughts:
Flashing headlights are illegal in most of the USA, too, not only in Washington.
Correct headlight installation is important to take advantage of shaped-beam headlights. They should be mounted at fork-crown or handlebar height. Mounting one lower, on a fork blade, would illuminate a smaller area too close to the bicycle; also, the wheel would cast a shadow in the headlight's beam. A battery-powered headlight may be supplied only with a handlebar fitting, and can be obstructed by the brake levers, hands, a rain cape or handlebar bag, but brackets are available to hold aheadlight below the handlebar stem.
Aiming the headlight is easy: the flat top of the beam pattern should go a bit below the horizontal.
If you're into do-it-yourself work, I've found that LED lights made to use with a generator will also work from the direct current of a 6-volt battery. That is convenient if you don't have the generator, or must use the light on a second bicycle..
A thought for the future: A couple of aiming features would be useful, but are not available:
Last Updated: by John Allen
