Join Date: Nov 2006
Location: NJ, NYC, LI
Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
You can get LED bulbs with the standard screw base, but they are a little problematic. They require DC current; but the dynamo puts out AC. They are brighter than the original bulbs, but the light source is not in the same place and this renders the original parabolic reflector pretty useless, negating the upgrade in power.
If you're willing to live with the latter problem, you can solve the former by putting in a bridge rectifier or, if you have both headlight and taillight run by the same dynamo, by reversing the polarity of one of the lights. That way, the single wire from the dynamo goes to the center contact of one bulb and the edge contact of the other; they'll light alternately and protect each other from reverse current.