pho·​ton | \ ˈfō-ˌtän How to pronounce photon (audio) \

Definition of photon

1 : a quantum of electromagnetic radiation Should a substance happen to have a lot of electrons in a higher level, and a lower level is mostly empty …, then a photon can cause an electron to transfer from a higher state to a lower one. This change releases energy and creates a new photon, in addition to the one which caused the transfer. This photon can in turn induce more electrons to fall to a lower state.— Robert Gilmore
2 dated : troland

Other Words from photon

photonic \ fō-​ˈtä-​nik How to pronounce photon (audio) \ adjective

Science and the Photon

It was Albert Einstein who first theorized that the energy in a light beam exists in small bits or particles, and scientists today know that light sometimes behaves like a wave (somewhat like sound or water) and sometimes like a stream of particles. The energies of photons range from high-energy gamma rays and X-rays down to low-energy infrared and radio waves, though all travel at the same speed. The amazing power of lasers is the result of a concentration of photons that have been made to travel together in order to hit their target at the same time.

Examples of photon in a Sentence

Recent Examples on the Web Any photon that emits in the wrong direction gets reflected to either strike the thermophotovoltaic device or be absorbed by the heating element, thus helping maintain its high temperature. John Timmer, Ars Technica, 14 Apr. 2022 First five-photon entanglement demonstrated by Jian-Wei Pan's group at the University of Science and Technology in China. Gil Press, Forbes, 14 Apr. 2022 And just like an electron, the antiproton can shift between orbitals by absorbing or emitting a photon. John Timmer, Ars Technica, 16 Mar. 2022 The electron can hop up to a higher-energy state by absorbing a photon whose frequency makes up the difference between the two states’ natural frequencies. Quanta Magazine, 26 Jan. 2022 An individual photon may be detected at any time over the entire pulse duration, which is now very long. Chris Lee, Ars Technica, 7 Jan. 2022 For every photon of planet light, a telescope sees 10 billion photons of starlight. Chris Wright, Wired, 4 Jan. 2022 Even an electron that’s just minding its own business can spontaneously emit and then reclaim a photon. Quanta Magazine, 22 Nov. 2021 Generating multiple electrons from a single photon gives greater sensitivity during image capture. Elizabeth Gamillo, Smithsonian Magazine, 10 Dec. 2021 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'photon.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of photon

1916, in the meaning defined at sense 2

History and Etymology for photon

phot- + -on entry 2

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Last Updated

22 May 2022

Cite this Entry

“Photon.” Dictionary, Merriam-Webster, Accessed 28 May. 2022.

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More Definitions for photon


pho·​ton | \ ˈfō-ˌtän How to pronounce photon (audio) \

Kids Definition of photon

: a tiny particle of light or electromagnetic radiation


pho·​ton | \ ˈfō-ˌtän How to pronounce photon (audio) \

Medical Definition of photon

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 candela per square meter

called also troland

2 : a quantum of electromagnetic radiation

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