Over the last ~10 years that High Brightness LEDs have been availible (and getting better), There have been a lot of people out there deciding to roll there own bicycle headlight/tailight due to: cost, form factor, function, weight, long run time, cool factor, etc. Here are my varied atemps at brighting the nite while i ride.
A older fit up in a "blank" using a luxeon star 3watt in a 1" by 1.25" housing/heatsink.
Notice the o-ring... i later found to be way over kill.
In these later models i've expanded to a different reflector and my skill at Al"welding" the mounting brackets is needing improvement (but still over kill).
Mounting the lights low is important for: stability, high lighting pot holes, getting them OFF the handle bars, and has the benifit of making you visible from the side. This image is of my commuter bike with 3 of the smaller older lights. This set up easly runs over 10 hours with a small pack of freecycled laptop batteries. The place to get battery fix em' up parts http://www.batteryspace.com
The newer designs i have used a Cree LED with a L2 Optic in a similar housing and mount to get more then 15 hour run time and twice as bright as the older designs.
Notice 1) the copper heat spreader plate the LED is soldered to, 2) the RTV strain relief on the wires, 3) Kaptan insulation under the LED conctact areas, 4) wire loop on the power leads to keep shock and vibe off contacts, 5) a step lip for a lens cover, no outer holding ring.
This design uses a tube instead of starting with a solid rod of Al.