Turning a Standard Bicycle Headlight into an LED Headlight

Summary

The Busch+Müller Lumtec Halogen bicycle headlight is used for this mod. At the time of writing, it's widely available across Germany, price starting from EUR 9.95
A side-emitting 1W LED (Lumileds Luxeon Emitter LXHL-DW01) is used as a light source.
The modification probably renders the headlight non-compliant to local regulations. Do this at your own risk.
This guide is applicable to other bicycle headlights of similar construction.

 Lumotec Halogen by Busch+Müller

Construction

Start out making the heat sink. Use an M10 bolt, a body washer, an M10 nut.
For optimum focus on a Busch+Müller Lumotec Halogen headlight, the visible length of the bolt's thread is 31.5mm . Other headlights probably require different length of the bolt to achive focus.
Cut 2 grooves (2cm long, thread-deep, starting at the tip of the bolt) into the side of the bolt. These are for the cables to the LED.

Heatsink

Remove the light bulb and coil spring from the rear part of the headlight.
Drill a 9.5mm hole exactly thru the center of the plastic part.
Bend the 2 contacts towards the front and solder thin wires to them.
Mount the heatsink thru the hole you just drilled. Apply 2-component glue on the thread, so the heatsink really stays there and doesn't turn.
Solder the LED to the wires (be aware of the polarity).
 Rear part before gluing the LED

Magnet pressing LED against bolt Now glue the LED to the end of the bolt with heat-conductive glue. I use silver-based adhesive made by "Arctic Silver". It's common in the computer industry.
Be sure that the LED is exactly centered vs the plastic part (this might not be the exact middle of the bolt !)
Once the LED is properly placed, you could use a neodym magnet to press the LED against the bolt until the glue has set.

Rear part before heatshrink

Push the cables into the grooves along the bolt and heatshrink them over.
Assemble rear part and reflector. You're done !

Rear part after heatshrink has been put Assembled Headlight

Electrically, this modified headlight is not compatible with a standard headlight.
For connection to a dynamo, pick an adequate circuit from the dynamo circuits page.

Note 1: Careful, dynamo and headlight might unexpectedly connect through the bike frame, shorting out part of the circuit.
Note 2: The Lumotec Halogen headlight contains an overvoltage protection diode. It's engaging above 9V. The LED voltage will never rise that high, so there's no need to remove it.

More Power

A 5 W version uses an LXHL-DW03 LED and a more massiv heatsink (brass bolt, 2 brass washers, 2 brass nuts):

5W Version 5W Version 5W Version

This is getting quite heavy (157 vs 51 gramm of the unmodified headlight)

Performance

Comparing an original headlight of the same type with the modified headlight, both running at 2.4 W (so I did this comparison with the 5 W LED):
The LED-version is much whiter but if shining onto dark ground, it's almost not brighter than the Halogen-version.

At very low power, the LED-version delivers more light than the Halogen-version.

The beam of the Halogen-version is vertically much narrower than horizontally. The LED-version's beam instead is nearly round and rather tight.

BACK