Short answer - no, the white wire will not work with a 20 Watt light. The magneto was designed to only make several Watts of power at 6 volts +/- of AC current, which is enough to run the engine and a low-power (3 Watts max) head & tail light system. You can run low-power LED lighting systems off the white wire, but the light output is relatively low and/or focused into a tight beam. You can run a 20 Watt incandescent lamp (like your photo) if you run it off a battery. You can trickle charge the battery from the white wire. Since the magneto makes alternating current, you will need at least one diode to rectify the current, but a full-wave bridge rectifier (basically 4 diodes) would be better. If you want to charge the battery properly, you should have a voltage regulator as well, but the extra cost may not be worth the trouble - try a single diode or a full-wave bridge rectifier (both available from RadioShack) with a small 6 volt lead-acid battery and see how well the simple system works for you....