Photon Definition

A photon is a packet of light or electromagnetic radiation.
A photon is a packet of light or electromagnetic radiation. picturegarden / Getty Images
by
Anne Marie Helmenstine, Ph.D.
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.
Updated July 24, 2017

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