This thread has given me the idea to make my own LED lights, so I've spent the last evening playing about. To ensure reliability and longevity for the white LEDs, I've used a proper constant current source. This is dead easy to build, just a single LM317L adjustable voltage regulator IC, a single 56 ohm resistor plus I added a 1N4001 diode to protect the circuit in case I accidentally swap the leads over (!).
I've wired 9 high brightness white LEDs in series (see circuit below) which works OK from 34V to about 55V. For use on lower voltages the circuit can be modified to use series/parallel strings of LEDS, as described in this application note:
http://www.onsemi.com/pub/Collateral/AND8109-D.PDF
For the rear light I'm using a flashing LED in series with seven high brightness red LEDs. This needs a constant voltage drive, so I'm playing about with easy and reliable ways to do this. I may post the results back here later.
Jeremy
Edited to add the rear light circuit diagram, which works a treat and is nice and simple. The flashing LED I used is voltage driven, so doesn't need a constant current source. To allow the array to work at 48V I used a zener diode to limit the available voltage - the value of this will need to be changed for a different supply voltage or different number of series LEDs.
Once I've finished gluing all the bits together I'll try and post a picture.