[I've tried the MR16 light route now, 3 12v in series from my bike supply. the internal rectifier works from 12v DC without reference to polarity, .ie. both ways. The problem is even with 3 MR16 lamps you get a lot of light up close but the standard 60 degree lamps don't penetrate far enough ahead. There's no need for e-bay as they are now available in the UK from electrical wholesalers under the Crompton brand.
Search for Cree bicycle lights on e-bay and there are at least 2 I have found. I've got a £4.99 version It works well for long range ( 30 /40 yards) and has a short range spillage area of low intensity. Try
shoujigift@gmail.com
These lamps use 3 AAA batteries they don't last very long, about 3 hours on full, but the best bike lights come with remote packs.
There is a more expensive focusable light, £19.99, this uses a remote 3 AA battery pack.
QUOTE=john;36462]You can get spot light versions of MR16. Mine are 25 degree spots which work well. Better to use two and a regulator rather than three as otherwise they could get dim as the battery voltage drops.[/QUOTE]
Still have not got far with this. However 60 degree lights would be hopeless and dangerous for oncoming cars. I am using a 24 and a 10 degree bulb. The piece I am waiting for is a digital light controller, this allows 2 bulbs to be used at different voltages and to overvolt as you need.
Having palyed a bit with this, the MR16 spot bulbs are great, especially the high efficiency ones like the IRC bulbs. Most bikes use MR11 but the MR16s are better due to the bigger reflectors. I wish I could find a 17 degree MR16 bulb but have not found one yet.
BM.