The Perfect Dynohub Headlight
What would the perfect bicycle headlight be? What would the beam be like? It should light up the road ahead of you evenly. It should enable other cyclists and motor vehicle drivers to see that you're there. It shouldn't blind oncoming cyclists, drivers or pedestrians. It should be on when you need it, and off when you don't. It should be powered by the rider, not by a battery. It should last forever, and cost you nothing. Unfortunately, it doesn't exist. But if you're willing to live with a few compromises, you can get pretty close.
Vertical Light Distribution
The beam should light up the road in front of you evenly. The road thirty feet ahead of you should be as brightly lit as the road 100 or 200 feet ahead. Not a little more or a little less, but the same amount of light should come back to your eyes from the road ahead at all practical distances. You don't care about the road a mile ahead, for example. How can that be done? If the headlight has the same light output in all directions, the road close to you will get a lot more light than the road further away. And even if the light is powerful enough that the road 150 feet away gets lots of light, if the road close to you gets a lot more light, then the contrast between close-up objects and objects far away will make those distant objects less visible to your eyes.
Consider how the light from your headlight hits the road ahead. Start with the headlight three feet off the ground. If the light were designed to illuminate the road from three feet ahead to infinity, the beam would have a vertical spread of 45 degrees. The top edge of the beam would extend forward parallel to the ground, at 90 degrees to vertical, and the bottom edge of the beam would touch the ground three feet ahead, and at an angle of 45 degrees to vertical. Now let's imagine the beam having two sections, the bottom half and the top half. The bottom half would be from 45 degrees to 67.5 degrees, half way to 90 degrees. and the top half would be from 67.5 degrees to 90. The bottom half of the beam would extend from three feet ahead to about seven feet ahead. The other half of the beam covers from seven feet ahead all the way to infinity. So let's think about this for a second. One half of our headlight's beam covers four feet of distance, three feet to seven feet ahead. The other half covers seven feet to infinity. That's a pretty big difference in the amount of ground each half of the beam needs to cover. So clearly, the top half of the beam needs to be brighter than the bottom half, if the two sections of the road each covers is to appear to the rider's eyes at the same brightness.
Now let's cut the top half of the beam in half, so we're now thinking only about the top two quarters of the beam. The top quarter extends from infinity, at 90 degrees to vertical, down to about 15 feet ahead, at 78.75 degrees, half way between 90 degrees and 67.5 degrees. The next quarter down extends from 7 feet to 15 feet, from 78.75 degrees to 67.5 degrees. And our lower quarter of this top half covers 8 feet of distance, 7 feet to 15 feet from the bike, and the top quarter covers from fifteen feet to infinity. So clearly, we see that the top quarter of the beam needs a lot more light than the second quarter from the top. And we could keep doing this, dividing the top part of the beam in half, and seeing that the top half always needs more light than the bottom, in order for the cyclist to see an evenly lit road surface. And every time we cut the topmost section in half, we're dealing with road that is further and further away, and dealing with smaller and smaller angular sections of the beam. The closer you get to infinity, the more light you need, and you need it over a smaller angle. It needs to be more concentrated.
So the ideal light, if you were to view it projected onto a vertical surface, rather than onto the horizontal road surface, would have an extremely thin and extremely bright top edge to its beam. And as you looked lower down that projected beam, it would become progressively dimmer. The extreme top edge of the beam would be for illuminating the road furthest away from you. It needs to be much brighter than the rest of the beam, since it's being projected further away from you than the rest of the beam. And the closer the road is to you, the less light it requires in order to appear as bright to you where you sit, on the bicycle.
And remember also that we don't want to be focusing light above the road surface; only onto the road itself. The reason for this is simple. The rider is providing the power for the light, and the rider doesn't care about lighting up the tree branches and sky overhead. And he doesn't want to focus light into the eyes of oncoming drivers. He wants the equivalent of the low beams in an automobile, lots of light on the road, and only spill light above the road, just enough so that oncoming drivers see that the cyclist is there. So as the light is projected forward, there ought to be a sharp cutoff between the bright light below the horizon, and very little light above the horizon.
Of all the dynamo powered headlights I sell, the one that comes closest to perfection in its vertical distribution of light, is the Schmidt E6. The key to the E6's performance is the tiny point source of light from the halogen bulb, and the highly advanced reflector. No LED light as yet produces such a thin and bright top edge to its beam, primarily because the source of light, the LED, is much larger than the tiny filament in the halogen bulb. The larger the point source of the light, the less precise the focused beam can be. So the E6 will light the road at a distance without having too much light closer to the rider, meaning that closer objects won't be too bright, relative to objects further away. So at high speeds, you're better able to react to whatever it is you're approaching; you have more time, because you can clearly see things further away.
Some folks believe that the only thing that matters is the total amount of light, and clearly the total amount is an important factor. But the distribution of light is also quite important, and shouldn't be sacrificed just to make a brighter light.
There are people who prefer a round, symmetrical beam for the bicycle's headlight. This would be like an automobile's high beam. For riding off road on narrow trails with tree branches to avoid, I heartily agree with them, and in fact it's what I use on my mountain bike. If you use a large diameter round symmetrical beam like the 5 watt Dinotte or Supernova E3 Symmetrical on the road, you can use it to best effect by aiming it a bit to the right, so that the beam that's focused above the road surface is aimed away from oncoming vehicles, and onto street signs. If the beam is narrow, like the 3 watt Dinotte, just aim the top of the round beam at the horizon.
It's difficult to compare headlights for total light output when there are so many beam shapes. When the Schmidt E6 was introduced several years ago, most people swore it was brighter than the Lumotecs they were used to. But since both headlights use the same bulb, we know for certain that they have the exact same total light output. By concentrating the light into a tighter beam, the E6 appears to be brighter, and parts of the beam are brighter. But the total amount of light is identical. The newest LED headlights not only appear to be brighter, they actually do put more light onto the road. The Inoled Extreme, Lumotec IQ Fly, Supervova E3 and Schmidt Edelux headlights are not only brighter, but also have larger beams. The power output from the dynohub is the same, but these lights are able to convert more of that electrical energy into light, and less into heat. So they are more efficient, and therefore brighter.
But total output alone isn't what will help you see further down the road at high speed. The distribution of light is extremely important as well. The brightest light isn't necessarily the one that will enable you to descend that steep hill the fastest.
What a very bright light can do for you is help you see where you're going when you're otherwise blinded by automobiles with cheap or poorly adjusted headlights, and particularly when you're out in the rain. Then it becomes a contest, and the cyclist always seems to fall short. But it's better to fall short by a little than by a lot when your life depends on it. If you're going to brave busy streets at night in the rain you'd be well advised to use the brightest light you can get. But quite frankly, better advise would be to find a quieter route in those situations.
When I regularly commuted 11 miles each way to work, the fast route was the main road, a numbered route west of Boston. But I never rode that route in bad weather. The back roads were hillier, windier and took an extra five or six minutes, but also a lot safer when the drivers had reduced visibility looking through a water smeared windshield. Remember that when you're on a bike in the rain, you can see much better than a car driver can.
The Tunnel Effect
If you're riding in the city, you have plenty of light from overhead street lights and other vehicles. You often don't need too much light in order to see where you're going, and you're more concerned with others seeing you. You need light on the road surface to see road debris and potholes, but you rarely need light in order to find your way. But out on the open road, there are usually no other sources of light. All you have is what you bring along, and perhaps what the moon provides.
On country roads on a moonless night, it's as though you're riding along in a tunnel. The width of the tunnel is determined by the width of your headlight's beam. The wider the beam, the wider the tunnel. With a narrow beam, you need to be paying closer attention to what's going on around you. With a wider beam, you can relax more. You don't feel as though you can make one false move, and go flying off the road. It's just more relaxing. But a wider beam requires more total light, otherwise that tunnel, though wider will be darker.
The headlights with the widest beams are the Supernova E3 (both types) Inolight 10+ and Extreme 30, followed closely by the Lumotec IQ Fly headlights from Busch & Müller (B&M) and the Edelux from Schmidt. Next widest are the Lumotecs and DLumotecs from B&M. The narrowest is the Schmidt E6. But you can run two E6 headlights side by side at speeds over 11mph or so, have plenty of light, and a nice wide tunnel. At lower speeds though, one would have to be switched off.
Reliability and Durability
LED headlights are inherently more reliable and durable, simply because you don't need to replace the bulb. There is no bulb to replace and LEDs last a very long time, up to 100,000 hours.It costs a lot more to make a light that's close to perfect than it does to make a light that's good enough for most applications. A good comparison is between the Busch & Müller Lumotec and the Schmidt E6 headlights. They both use the same halogen bulbs and so they both have exactly the same total light output. You can think of the E6 as a highly refined version of the Lumotec. For example, the B&M light has a simple but effective plastic slider switch that, for most people, will last for many years of daily use. I've sold thousands of them, and only had a couple fail. Schmidt uses a magnetic reed switch. It's activated by a magnet embedded in a plastic ring that slides around the outside of the housing. The switch itself is safely inside the aluminum housing. It's designed to last indefinitely. And in practice, they never fail. The switch is just one of the advantages to the E6 over the Lumotec. But the E6 costs several times what the Lumotec costs. So the Lumotec has to be considered the better value, for most cyclists. And it should come as no surprise that we sell more Busch & Müller headlights than all the rest combined. The new Luceo LED headlight from Spannninga is another high value light.
Some hub dynamo headlights are simple On/Off types. They have a two position switch. Others have a three position switch; On/Off/Senso. The Senso position uses a light sensor. When you're moving, and power is available to the headlight from the hub, the light sensor will switch the light on and off. These are designed so as not to be fooled by the lights from automobiles.
Some lights also have a Standlight. Ordinarily, when you come to a stop, the headlight goes out. But some lights have a capacitor which stores electricity like a battery, and when you stop, the electronics inside the light switches on the Standlight, giving you light for anywhere from four to fifteen minutes, depending on the particular model. The Standlight is always dimmer than the running light, but is bright enough that others will see that you're there.
Headlights without a Standlight are the Schmidt E6 and any Busch & Müller headlight without the word "Plus" in the name. Headlights with a Standlight are all Busch & Müller headlights with "Plus" in the name, all Inoled headlights, the Supernova E3 and the Schmidt Edelux.
Headlights without a Senso function are all B&M headlights without the word "Senso" in the name, all Inoled headlights, the Supernova E3 and the Schmidt E6. Headlights with the Senso function are all B&M headlights with the word "Senso" in the name and the Schmidt Edelux.
Right Side Up!
All dynamo powered headlihts and taillights must only be used right side up. Do not use them upside down. Not only will the focusing of the headlight beam be ruined by reversing the headlight, but using the light upside down can allow water to get inside and stay inside the light. Even the Schmidy headlight, which is well sealed against water entry can fail if used upside down. This is because the electrical connection for the taillight, on the base of the Schmidt Edelux headlight, is in a recess on the bottom, which, if the light is upside down, can fill with water, creating a short circuit. Most of the other headlights and taillights are sealed at the top, and open at the bottom to allow any condensation to drain out. We never have problems with this, as long as the light is mounted right side up.
What does "right side up" mean?
For a headlight, it means that the part of the light housing that attaches to the mount is located at the bottom. And any wires that attach to the light housing are also located at the bottom. For a taillight, just look at any name on the housing, and align so the text is right side up.
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This page updated: Friday, January 18, 2013
Peter White Cycles