Does any body know, if there are restrictions about carrying a flashlight in the pocket or in the hand baggage in an airplane. I can imagine Li-Ion batteries could be a problem. What are the guidelines / suggestions for that?
For li-ions i expect them to be cautious if you carry a moderate quantity. Single cell flashlight is not a greater threat that a pda, cell phone or laptop.
I've made four flight trips with li-ion powered flashlight is my pockets, never had a problem with security. One time at the security checkpoint an airport security agent managed turn the light on while pointing it towards her own face. It was a smooth p60 W/ XRE R2. Silly airport security agent, never turn on a LED light while it is pointed directly towards your own face.
I could imagine that the security checkpoint would cause problems if you bring a lot of spare cells. The amount of lithium you are allowed to bring on board is limited. Just bring a charger and a smaller number of spare cells and you'll be fine. Or just avoid lithium powered lights altogether, there are plenty of powerful AA lights around nowadays.
I think if you feel the need to carry anything beside whatever is already attached to your keychain than you have serious flashoholic problems .If the plane crashes ..i doubt you'll be looking for your quark. the only light you'll be heading for is down that really really long hallway . Carry a book on the plane . put lights in your bag.
The long dark corridor filling with smoke and other passengers? Then I'd rather have a quark than a book : )
I wouldn't be flying at all if the risk of crashing were the reason for me bringing that light. Flashlights are useful when searching for stuff in the dark when you finally arrive at your location in the middle of the night. Searching a dark bag for a light would kind of defeat its purpose.
And, more importantly, a lot of hotels here attempt to show some "greenness" by putting ludicrously low-power CFL bulbs in light fittings. The last hotel I stayed in required a flashlight to find the power point even with all of the (5W CFL) lights on. And it is rather hypocritical putting wildly inadequate bulbs in while heating the place to an unbearable temperature (In winter). And I work in a hospital and spend my working days in places over 30oC.