Mechanically powered flashlight
They are considered a green technology, because the disposable batteries used by ordinary flashlights are wasteful in terms of resources used for the amount of energy produced, and also contain heavy metals and toxic chemicals which end up in the environment.
The user repeatedly squeezes a handle to spin a flywheel inside the flashlight, attached to a small generator/dynamo, supplying electric current to an incandescent bulb or light-emitting diode.
[2] The photo shows the internal mechanism: the L-shaped handle has a gear rack, which spins the white step-up gear, which in turn spins the flywheel on which is mounted both a centrifugal clutch (to allow freewheeling after the lever stops its travel and then returns) and a dark grey magnet, seen on the lower left.
This design contains a linear electrical generator which charges a supercapacitor which functions similarly to a rechargeable battery when the flashlight is shaken lengthwise.
The linear generator consists of a sliding rare-earth magnet which moves back and forth through the center of a solenoid (a coil of copper wire) when it is shaken.
A current is induced in the loops of wire by Faraday's law of induction each time the magnet slides through, which charges the capacitor through a rectifier and other circuitry.
This, along with the long-life light-emitting diode which does not burn out like an incandescent bulb, give the flashlight a long lifetime, making it a useful emergency light.
A disadvantage of many current models is that the supercapacitor cannot store much energy in comparison to a lithium-ion cell, limiting the operating time per charge.
These fraudulent flashlights eventually become useless, since their internal batteries cannot be recharged or replaced, and the case is often permanently glued shut.
The purpose of this design, originally invented for use in the developing world, was to improve its reliability and useful lifetime by avoiding or reducing reliance on a battery.
They may also include alternative means of charging the battery, such as an AC adaptor, solar cells, or cords that plug into a cigarette lighter socket in a car.
The quality and long-term reliability of these devices vary over a wide range, from high-reliability mil-spec emergency equipment down to one-time-use non-repairable disposables.
