is an example of a quantum experiment that uses wave-like behavior to accumulate to a particle-like behavior. in the experiment the intensity of the light used is insignificant, where as the wavelength and or frequency of the light is significant. the energy imparted to electrons bombarded by light is found to be done in discrete quanta such that individual photons of a given frequency are 'absorbed' by the electron putting the electron into a higher energy state. if the electron 'falls' to a lower energy state it emitts a photon whose frequency matchs the amount of energy lost. for some reason and i wish i knew what that reason was, a moving electrical charge emitts light.
regards, tim