to add to the above, the lights he is talking about use coin cell Lithium type batteries, which will still work to about 0*F but if the light itself is going to get -20 to -40*F chances are the battery is going to have issues.
hmm, if i remember right the only consumer type of battery that will work in that extreeme of a condition is a Zinc-Air, and they would have other issues, like thin air, and would still be weaker when cold.
so lithium is probably your best bet.
human breath headed to the mic, and heat comming off the human should have the temps usable for lithium.
a photon (type) light will do 30 strong hours of very low light , the newer ones might have a bit more SPOT then they want, but the led could be changed or diffused as needed. they burst up when you first turn them on, then the smaller weak batteries will have the light drop a bit as it stays on over time.
are they going to want colored light?
do they need to read maps with important colorations on it?
Is the light needed for continous use or intermittant?
what kind of power would they need?
spot or flood?
i would mention a very lightweight headlamp instead, like a 4led adjustable level headlamp, if i didnt already know how clunkey and huge and weighty the headsets are. or a headlamp with both white and red leds.
a really neet trick would be to drive the light off the headsets power, because half of them headsets connect to the planes power already, making it available right there . a modification, there is even room in the mic unit itself for the leds to stick out of the plastic. i bet in 10 years plantronics or somebody will build it right in.
but then what do you do when the plane power fails and you still need to fly ?