- Also called photon. A particle with no mass nor charge, and which composes light and other forms of electromagnetic radiation. gamma rays and X-rays are examples of higher-energy photons, while infrared rays and radio waves are examples of lower-energy forms. Its energy is equal to hf, where h is the Planck constant, and f is the frequency of the radiation in hertz. Photons are required to explain phenomena such as the photoelectric effect, in which light has particle-like properties. The photon is the carrier of the electromagnetic force, which is the force responsible for all electromagnetic interactions, such as those which hold atoms and molecules together.