Photoelectric Effect See also: Photoelectric Cell; Quantum Theory The emission of electrons by substances, especially Metals, when Light falls on their surfaces. The effect was discovered by Heinrich Hertz in 1887 and explained by Albert Einstein in 1905. According to Einstein's theory, light is composed of discrete particles of Energy, or quanta, called Photon(s). When the photons with enough energy strike the material, they liberate electrons that have a maximal Kinetic Energy equal to the energy of the photons less the Work function (the energy required to free the electrons from a particular material).