This comprehensive programme tells the story of the discovery of the photoelectric effect, its investigation and eventual explanation by Einstein, which brought about the revolutionary notion that light is a stream of photons and the development of quantum mechanics. The programme covers: * Hertz's initial experiment * Lenard's investigations of the p.e. effect * Evidence for the wave theory of light * Problems with wave theory when explaining p.e. effect * Plank's explanation of black body radiation * Einstein's application of Plank's theory to the p.e. effect * Calculations of threshold frequency, cut-off potential, work function * Applications of the p.e. effect