A photon is a tiny energy packet of electromagnetic radiation, also referred to as a light quantum. Albert Einstein's account of the photoelectric effect, in which he proposed the existence of discrete energy packets during the transmission of light, gave rise to the concept of the photon in 1905. Einstein reasoned that the momentum (h v/c) of the light quantum may also be related. The possibility of the light quantum being connected to a particle was strongly suggested by a significant energy value and momentum. Later, the photon was given to this particle. A discrete bundle (or quantum) of electromagnetic (or light) energy is therefore described as a photon. Photons move at the speed of light (3 108 m/s) because they have no mass.