## Light Photons

Light has been studied by leading scientists since Newton’s investigation of it in 1675. It is still not fully understood.^{32} It acts like both a fundamental particle and an electromagnetic wave.^{33} The photon is a unit particle of light, an element of radiant energy, according to the quantum theory: a light quantum. It has a momentum equal to its energy divided by the velocity of light and moves as a unit with the velocity of light.^{34} A quantum is the smallest amount of energy capable of existing independently.^{35} The quantum theory based on Planck’s radiation law that changes of energy in atoms and molecules occur only in discrete quantities.^{36} Ordinary light is emitted by atoms.^{37}