Depending on how you choose to build the torch, you can have anything from a pencil beam with a range
of at least 50 metres (and incredibly, it will light reflectors at well over
five times that distance!) to a broad and diffuse light source perfect as a
general purpose torch.
Plus, you don't need to turn the handle continuously; the light
itself is ultra-white; and we would expect such a torch to last for, well,
And, to top it all off, if you play your cards right, the torch
can also cost you very, very little to put together...
The Design Basics
So what's inside these human-powered torches? Just four basic
components: a stepper motor, which generates the power to run the thing; a
rectifier, which converts the AC (alternating current) from the stepper motor
into DC (direct current), which the LED needs; capacitors, which store the
power; and finally the LED itself, which produces the light.
These human-powered LED torches have some really good emergency applications. The light is visible from a very long distance (especially if you build it to have a narrow, focussed spot beam) and the torch will never get a flat battery. Because of the direct-drive system, the quality bearings used in stepper motors, and the LED light source, the torches should also have an almost unlimited life.