A crank powered torch

The phenomenon of electromagnetic induction involves generating of electric currents in a circuit, if the magnetic field closed inside this circuit changes. We say that an electromotive force emf is induced and causes the electrical current flow.

This phenomenon was discovered by Michael Faraday (and independently Joseph Henry), inspired by Christian Oersted's who showed that the electric current creates a magnetic field around.

Faraday noticed that the decisive factor for the emf amplitude is the velocity of the magnetic flux F_B changes.

and if the circuit contains N wires it is:

Therefore, moving the lamp up and down faster (or cranking up harder in the other type lamp) creates bigger currents. The number of wires in the induction coil is also important.