photon

noun

pho·​ton ˈfō-ˌtän How to pronounce photon (audio)
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
photonic adjective

Did you know?

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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Named after the famed physicist John Stewart Bell, the test measures pairs of entangled photons with properties that remain correlated even after separating across huge distances. Andrew Paul, Popular Science, 12 June 2025 While a sailboat harnesses the lift created by wind flowing over its curved sails to move across water, a solar sail uses the momentum of photons from sunlight, reflected off its large, shiny sail, to propel a spacecraft through space. Mojtaba Akhavan-Tafti, The Conversation, 11 July 2025 In this method, two photons enter a state of entanglement. Reed Albergotti, semafor.com, 24 June 2025 The thought melted into another: The tiny sliver of photons that somehow do find this observatory will be pretty special. Michael Jones McKean, The Atlantic, 23 June 2025 See All Example Sentences for photon

Word History

Etymology

phot- + -on entry 2

First Known Use

1916, in the meaning defined at sense 2

Time Traveler
The first known use of photon was in 1916

Browse Nearby Words

Cite this Entry

“Photon.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/photon. Accessed 21 Jul. 2025.

Kids Definition

photon

noun
pho·​ton ˈfō-ˌtän How to pronounce photon (audio)
: a tiny particle or bundle of electromagnetic radiation

Medical Definition

photon

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

More from Merriam-Webster on photon

Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!