vr,
The website vixen2yall provided has a discussion of running halogen bulbs (MR-11 and MR-16 mainly) overvoltage, which is running 12V lamps with a battery providing 13.2V (10% overvoltage) or 14.4V (20% overvoltage). Light output is increased MUCH more than the 10 or 20%. Though bulb life is shortened significantly, light output increases dramatically. The shortened bulb life is not a big problem since most halogens are rated for 2000-4000 hours anyway. He concludes that overvoltaging up to 20% can be a great way to increase light output. You do have to make sure your other components, like switches, can handle the increase. Hitting a bulb with extreme overvoltage will cause it to burn out immediately.

Your light 19V battery may be attractive to use, but getting bulbs may be difficult and expensive. Check some places like lightbulbsdirect.com to see if you can find bulbs around 18V or so. And keep in mind that you may not find a bulb shape that has a practical light fixture for use on a bike. To me the attractive thing about using 12V components is that you can get any parts you need from local sources like Auto Zone, Radio Shack, and Home Depot at inexpensive prices, and you have so many choices. For my purposes, going with an unusual voltage defeats the purpose of taking the trouble to put together your own system.

Just one old fat guy's take on it.
Regards,
Raymond