Ah, well, the only light combination that I've personally used that has matched automobile headlights is a Light and Motion 900 on High, while also running a Light and Motion 1400 on medium. If I remember right, runtime is more around 2 hours, not to mention it's really expensive. And it will most likely blind the heck out of anything else you're biking towards.

As mentioned earlier the Busch and Mueller Big Bang is the only light I know of that is high powered and has a cutoff.

I had forgotten about the E3 triple - it's to bright and floody for bike trails, but it would probably be fine on the street. But if akrejci says the Luxos is better...

Unfortunataly I'm just not sure that there's a solution to your problem... :-(

P.S. In theory, if you can find a battery light that charges via usb and also runs while charging, you could get an external battery pack. They sell external usb power sources on amazon, and they're not even terribly expensive. But I don't think it's easy to find a light that will actually stay on while the usb power is plugged into it...