Note: This was written in 1992 and has not been updated since. I no longer use this headlight.

Why I Made a Headlight

When I started looking for a good headlight for winter commuting in the rain and fog of Puget Sound, I saw two classes of light: grossly underpowered, and grossly overpriced. Determined to find a middle ground, I looked for sturdy fixtures in local hardware stores and auto parts stores. After consulting lightbulb catalogs and checking application notes, I settled on a 20 watt halogen landscaping light made by Toro. The fixture with one bulb cost under $20. Its full name is the "Toro Varifocus MiniSpot Light," model #52985.

If you need less power, there are many other models of low-voltage landscaping lights available, from 5 watts up. If you want more power, you might want two of these 20W lights with one on a switch for a high/low beam effect. All the landscaping light systems I've looked at use 12 volts, so batteries are easy to get.

I considered but rejected as too heavy and/or bulky a variety of automotive fixtures, also in 12 volts. For those with a real craving for light, motorcycle equipment looks promising.

Power Supply

The light requires 12 volts, meaning it draws 1.67 amps for 20 watts. For my goal of a three hour run time, then, I needed 5.0 amp-hours. To be on the safe side, and because it was on sale in a mailorder catalog, I decided to use a 6.5 Ah lead-acid gel cell. This is about the size of a brick, but heavier, and cost $32. Theoretically, at 1.67 amps it should give me about 3.9 hours between charges. Runtime declines in cold weather, but keeping the battery insulated helps.

To charge the battery I used a 12v battery eliminator from an old radio. With no load this actually puts out a little over 13 volts, but it can't put out more than 500 mA, which makes it a fairly safe charger for unattended overnight use. Faster charging is safe if you buy a good charger, or monitor the battery to prevent overcharging, but I took the easy way out.


For a switch I got an in-line extension cord rocker switch from the local hardware store. It's rated 15A @ 130v, so it can easily handle 1.67A @ 12v. It is not waterproof by any means, but at only 12v there does not seem to be any problem with shorting or electrolysis.

Finally, to wire everything together I used plain 16 ga. zip cord. For quick-release connections I used 1/4" mono plugs and jacks, primarily for their great resistance to abuse. To make the connections somewhat water resistant, I put lengths of small-diameter bicycle tubes over the inline jacks and plugs, with about 1/4" of overlap. This setup worked well enough when I carried the battery on the front rack along with the light, but the 1/4" plugs unplugged too easily on longer cords, so I switched to polarized automotive quick-disconnects. These are also very abuse resistant, and also weigh less than metal 1/4" inline connectors.

The battery wiring harness has two legs. One plugs into the light cord, the other connects to the charger. This lets me leave the charger connected and just drop it into the pannier next to the battery. I've considered a modification for touring that would charge the battery from a generator run through a rectifier and voltage regulator. A friend suggests a small solar panel charger mounted atop the rear rack, but I'm not sure how much good it would do in the Puget Sound area -- direct sunlight is rare much of the year.

A FUSE IS IMPORTANT: batteries like this can briefly put out hundreds of amps when shorted, which is enough to set the wiring on fire, do spot welding, etc. Un-fused wiring is not worth the time and money it saves. I have an inline fuse holder on the battery's positive terminal, before the Y where the lighting leg and charging leg split. I use a 10 amp slow-blow fuse to allow considerable leeway for user stupidity yet still protect the battery and wiring.


Once I had all the parts together I had to figure out a mounting system. The light fixture is designed to mount on a plastic stake in the ground, but the bolt that holds everything together is a standard carriage bolt. I have tried various mountings for the light itself. Currently I have a 6" carriage bolt stuck through a hole in the flat center support of my Blackburn front rack. Above the rack is a standard nut; below the rack is a broad washer and a wingnut. Spinning the wingnut off lets me remove the light in under a minute. To stiffen the long bolt, I have nylon spacers held tight with another pair of nuts.

This placement of the light does several things. It puts the light 6" above the top of my front rack, so that loading the rack does not block the light. Also, the higher position gives slightly better lighting at a distance. Finally, only the bolt obstructs the rack, rather than the entire light fixture, so there is room for my ever-present waterproof radio. (The light even doubles as a dial light so I can zap the commercials on the way to work.)

The battery is in a bag I sewed up out of nylon pack cloth. I made long flaps on the closure to avoid water intrusion, and put on velcro hanging straps in three directions so I can hang it just about anywhere. That way I can move it around if I need to counterbalance unusual loads on the front or rear of the bike. Because temperature affects battery performance, and also to avoid cracking the plastic case of the battery, the bag is lined with 1/4" neoprene foam from a long-dead wetsuit.

For better balance, I keep the battery on the front of my rear rack. Originally I carried it in front with the headlight, but I prefer not to have the extra weight over the front axle. Some day I intend to make a sturdier battery carrier that will mount on water bottle bosses, getting the weight even lower and more centered on the bike.

After some trial and error, I decided I like the light set near the long end of its focal range for average riding, though this varies depending on the weather, traffic, and road conditions.


A 20W halogen lamp is plenty bright enough for most riding. I light up roadsigns from more than half a mile away, and can see the road surface in adequate detail for 25mph riding, even when the ground is wet. There are still some times when the light can't overcome the weather completely -- last winter (Dec. '91) I was riding in fog so dense I could not see the ground beneath my front wheel, and the light would only show the fog line for 10 feet or so ahead of me. Fortunately, I had remembered to put on my fog strobe as well as my Vistalight that morning, so traffic could still see me from behind. As unnerving as dense fog is at first, I actually feel safer on my bike than in my car, since road feel and hearing are much better when cycling and aren't hurt by fog.

I'm still on my first light bulb, so I don't know how long they last. The spare bulb is very small, about the size of an ordinary flashlight bulb. As with all halogen bulbs, it is important to keep the bulb clean, so I carry the spare in its blister-pack wrapped in a small cotton rag for installation.

Future Modifications & Improvements

Apart from the charging options and battery mounting discussed above, I've considered a number of changes. First among them is a tail light. I know I'm very visible with my existing reflector-mount amber Vistalight, but I may still add a steady red light. Some drivers have complained to me that just a Vistalight is somewhat disorienting, since there's nothing for the eye to hold onto between blinks. This may be an advantage -- I'm not sure. The unknown may get wider clearance than the known. I'll have to think about this more.

I may someday add either a simple dropping resistor or some more complex electronic dimmer to extend the battery life, since many times I don't need the full 20 watts. On the other hand, every addition is another source of potential breakage, so maybe I won't.

This page written by Joshua Putnam. Please feel free to email questions, comments, corrections, suggestions, etc. Josh Putnam's Home Page | Josh's Bike Page. | Josh's Framebuilding Page. | Josh's Photo Page.

© Joshua Putnam