photon

In physics, the elementary particle or ‘package’ (quantum) of energy in which light and other forms of electromagnetic radiation are emitted. The photon has both particle and wave properties; it has no charge, is considered massless but possesses momentum and energy. It is one of the gauge bosons, and is the carrier of the electromagnetic force, one of the fundamental forces of nature.

According to quantum theory the energy of a photon is given by the formula E = hf, where h is Planck's constant and f is the frequency of the radiation emitted.