High Intensity Discharge (HID) flashlights.  Incandescent flashlights have a bulb with a filament, much like the common household light bulb.  A consistent amount of current is fed to the bulb.  The filament glows and light and heat are produced.  The filament glows because it is a poor conductor of electricity.  Eventually the filament breaks due to vibration or diminished capacity.  HID flashlights have a globe of gas that contains bounded by electrodes.  A spark jumps across the electrodes igniting the gas.  Initially, the amount of current required to ignite the gas is higher.  Once the gas is lit, much less current is required to keep the gas burning.  A device called a ballast controls the amount of current sent to the bulb.  HID flashlights use about 50% less energy than incandescent bulbs, which means longer battery life than halogen incandescent bulbs.  More importantly, HID lights have no filament to break.