I tried the backpacker's headlamp, and while it's a huge improvement over the old dead-battery-storage-cylinder of a traditional flashlight, the headlamp can be far too bright, even on the dimmest setting, for good dark adaptation.
Then last year I bought a ball cap with three little LEDs embedded in the leading edge of the brim from Eddie Bauer. Not sure they still have them, but what a find for flying! A button in the brim cycles through the choices- two on, all three on, and all off. I painted red nail polish on the first two, so that I get a soft pink glow which is bright enough to illuminate wherever I'm looking, but not so bright as to wreck my dark adaptation. With all three on, it's good to preflight at night, read the tiny print on the charts, etc. It's my all-purpose flying hat now, to shade my eyes from late afternoon sun, then when it gets dark, my flashlight is right there, looking where I'm looking. Don't know how long the replaceable battery lasts, but I've been using this one for a year now, and highly, highly recommend it.
I don't see this exact one, but there are several choices available by googling LED ball cap.