HID! If your serious about night duning HID is the only way to go. I had Ricky Stator make me a custom set up for my TRX. A few pic's of the set up towards the middle of this page:
http://www.sandbros.com/mikes_ride.html The cost is high but it's worth it!
He may have a bulb that fits in the stock housing (pretty sure he does for the TRX's). You'll need your stator altered and need a battery.