Actually I am an EE which is probably why I'm having so much fun with this project.

The 12V AC spec implies (at least to me) that there is definitely some type of bridge and voltage regulator inside the bulb package. Remember that the actual physical diode will never have a voltage drop more then a few volts, so they have to control this somehow. A heat test showed that after 15 minutes in my garage the package was not noticeably warmer. LED's are primarily killed by heat, the reason that we're getting increasingly bright LED's is primarily better designs for heat dissipation. Since they're all rated for 10's of thousands of hours, a bike light that reduces the life span by as much as 90 percent is still good for the 100 hours or so I use it per year. It would be nice if one could get a schematic of whats inside but I'm not goning to hold my breath.

I'm kinda hoping the 3 watt bulb fails first so I have an excuse to buy another 6 watt.

The concern for battery life is real. But LIPO battery's are only good for a couple of hundred recharges in a year or maybe two any way, before they're at 75% capacity. I'm planning on Woot having the XP16000 on sale by then!

Thanks for your comments!!!