Science, Tech, Math › Science Photon Definition Share Flipboard Email Print picturegarden / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated February 01, 2019 Photon Definition: A photon is a discrete packet of energy associated with electromagnetic radiation (light). A photon has energy E which is proportional to the frequency ν of the radiation: E = hν, where h is Planck's constant. Also Known As: quantum, quanta (plural) Characteristics Photons are unique in that they have characteristics of both particles and waves at the same time. For students, it remains unclear as to whether a photon is a particle that travels in a wave pattern or a wave broken up into particles. Most scientists simply accept the photon as a unique packet of energy that has characteristics of both waves and particles. Properties of a Photon Behaves like a particle and a wave, simultaneouslyMoves at a constant velocity, c = 2.9979 x 108 m/s (i.e. "the speed of light"), in empty spaceHas zero mass and rest energyCarries energy and momentum, which are also related to the frequency (nu) and wavelength (lamdba) of the electromagnetic wave, as expressed by the equation E = h nu and p = h / lambda.Can be destroyed/created when radiation is absorbed/emitted.Can have particle-like interactions (i.e. collisions) with electrons and other particles, such as in the Compton effect in which particles of light collide with atoms, causing the release of electrons.