These flashlights come in a variety of shapes and sizes, but they all share five basic components. They all have a crank, magnet, wire coil, an energy storage device and a bulb or LED.
The device works by electromagnetic induction, which is a lot more simple than it sounds. Typically, when you turn the crank, it spins the magnet within the wire coil. As the surfaces pass each other repeatedly, electrons are pulled from the magnetic field, creating electricity. The electric charge passes through the wire coil to the storage device (either a battery or capacitor) which then powers the bulb.
How effectively these flashlights generate and store energy can vary greatly depending on the quality of the tiny generator. The norm is about 30 minutes of light generated by 30 to 60 seconds of cranking.
Due to the self-powered nature of the flashlights, there is a tendency to think they will last forever. Over time, however, the internal storage battery or capacitor can become less efficient in holding power and eventually can fail.
These hand-held helpers can light your way plus a great deal more. An array of hand crank equipment is available that combines flashlights with AM/FM radios, weather radios, clocks and cell phone chargers.