Tis is an older thread, but worth adding to.
I've used Sylvania's H4 SilverStar xenon bulb to replace the hi/low beam bulb in the stock Triumph headlight reflector. It gives a much brighter, whiter light that extends further down the road. While a friend tried it on his HD and it only lasted him 5 months of shaking, I'm only on my 2nd bulb after riding with it for almost 6 years. Just make sure the one you buy specifically says (for Motorcycles) on the single bulb package as it's built a bit more rugged. I don't think he had the MC bulb - it takes a bit of searching the auto parts store to find it.
Sylvania rates the bulb at 910/1,500 lumens and has max. 65/72 watts with a 4,000 K (bright white) color temperature. It's a plug and play replacement - just replaces the stock bulb and the stock wiring and switch has not shown any problem at all. I use the hi beam during the day, figuring if I loose that filament, I still have low beam which will be OK to ride with if my ride takes me into the night. I adjust the headlight aim like a normal headlight and the hi beam use during the day doesn't seem to be an issue with oncoming cagers. It's the best $20 lighting improvement I've seen.
