Fuller and Pearson placed a thin layer of the first type of doped silicon (extra electrons) atop a layer of the second type (extra holes). The two Bell researchers attached the little assembly to a circuit--a loop of wire, in effect--and an ammeter, a device that measures electric currents. When they turned on a desk light, the ammeter showed the two-layer silicon suddenly generating an electric current. The same thing happened with sunlight. Fuller and Pearson realized that the photons were penetrating the top layer with enough force to knock electrons into the bottom layer, creating a flow of electrons that moved into the wire: a current. The two men had accidentally created a new type of solar panel.