For Â£40ish: 2x 4000mah nimh battery packs (eBay etc), 1x MR16 outdoor/garden 12v light. Li'l bit of time with a soldering iron etc & a bar clamp from any old sets of lights you have lying around... You'll need a charger too, but it's a cheap way to some very effective lights!
14.4v over-volted halogen lamps give out $hit loads (technical term!) more light at the expense of reduced life - ie 100 hours rather than 1000 or something. Either way, the lamps themselves cost pence so who cares?!
35w (at 12v - more at 14.4!) lamp burns for about 1.5 hours & is BRIGHT!
50w lasts less time & is unnecessarily bright.
20w burns for 2.5ish hours, & is significantly brighter than a 'normal' 20w lamp!
Obviously bigger batteries'd last longer, but the 35w lasts more than long enough for an average night ride for me...
Ride slow for FeAR of FLYiNG PAST dReAMS
Fat Buckshaver, SC Heckler, Prof 856, Orange P7