A simple, functional home-made headlight mount

December 3, 2010

Headlight mounts always end up looking a little clunky, and are a little hard to adjust. This one works better than most I’ve tried, and looks better too (at least, relative to the others). You’ll have to take it on faith that the shape is pretty good, but the shape is pretty good, meaning, it throws a lot of light down the road, not too much too high, and makes a nice puddle around the front of the bike. I solve the light-in-eyes problem with low-beams; this one’s not too bad, but the amber low beams, mounted low, aimed low, are vastly better.

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The basic ingredients are:

  • 2 bell mounts. You need to size these for your handlebars; the smaller size that fits traditional mountain and upright bars is easy to find; the kind that fits road bars (in this picture) are a little harder.
  • 2 long (metric) bolts/screws and 4 washers and nuts. This holds the lights out from the bars, leaving room for cables etc.
  • Acrylic mirror “hat”. This keeps light out of your eyes, and keep some of the light out of other people’s eyes, and directs light down at the road. It also keeps rain from falling directly on the LEDs.
  • LEDs and lenses. Get good ones. These are CREE XP-G, 139 lumens each at 350mA, triple that at 1 Amp.
  • Aluminum angle stock. This holds it all together; the bolts are bolted to it, the mirror is epoxied to it, the lights are epoxied to it. A tight joint with the LEDs is necessary because this is also their heat sink. At full power (1 Amp), not moving, this is not an adequate heat sink; moving through the air makes a huge difference.
  • P-clamp and switch. Modern white LEDs are so bright and annoying that a civilized, considerate cyclist will add a second set of lights for use around other cyclists and pedestrians. This is the nicest mount I’ve cup up with so far; the switch (a small one) is bolted directly through the P-clamp.

Minor improvement — flip the angle bracket around, so that the mirror is glued on behind the lights. This puts mirror directly above the LED, which kicks a bit more light down, and also allows you to clamp the mirror in place with a bulldog clip instead of epoxy (mirrors can break).

Aiming and shaping the light is a bit of a trick; the larger the mirror, the sharper the cutoff, but too sharp, and drivers in trucks might not spot you. A little bit of upward slop is necessary. It’s also nice to send a good bit of light far down the road, so that you illuminate signs and get early warning of pedestrians and unlit cyclists. This mirror is designed to let the spot slop upward a bit, but cuts off the flat/wide a little more, especially straight ahead. The whole light can be fine-tuned left/right by adjusting the nuts on the angle-iron, and it can also be leveled and aimed easily.

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