Light is both a high-frequency electromagnetic wave and a particle flow composed of elementary particles called light particles. Therefore, light has both particle and wave properties, or it can be said that light has "wave-particle duality". Photon, formerly known as light quantum, is the basic particle that transmits electromagnetic interaction and is a gauge boson. Light particles are the carriers of electromagnetic radiation, and in quantum field theory light particles are considered to be mediators of electromagnetic interactions. Compared to most elementary particles (such as electrons and quarks), light particles have zero rest mass, which means they travel in a vacuum at the speed of light. Like other quanta, light particles have wave-particle duality: light particles can show the refraction, interference, diffraction and other properties of classical waves; while the particle nature of light particles does not behave like classical waves when interacting with matter. Any value of energy can be transferred, and light particles can only transfer quantized energy, that is: Here is Planck's constant, which is the frequency of the light wave.