I replaced the standard headlight on my home made 'Alleweder' Velomobile with two Luxeon power leds with two different lenses, one for a small bundel for long distance illumination, the other with a broader bundle for close distance.
Step 1: Parts Needed
Step 2: Mark Position of Leds and Lenses on the Heatsink
Step 3: Place the LEDs
Then screw the LEDs on the heatsink, and solder them together in series.