In physics, a corpuscle of energy or particle of light; a quantum of light or other electromagnetic radiation.
* * *
pho·ton 'fō-.tän n
1) a unit of intensity of light at the retina equal to the illumination received per square millimeter of a pupillary area from a surface having a brightness of one candle per square meter called also troland
2) a quantum of electromagnetic radiation
* * *
pho·ton (foґton) [Gr. phōs, gen. phōtos light] a discrete particle with no mass and no charge, the quantum electromagnetic radiation.Medical dictionary. 2011.