photon

noun

pho·​ton ˈfō-ˌtän 

1

: a quantum of electromagnetic radiation

Light is made of particles called photons, bundles of the electromagnetic field that carry a specific amount of energy.

—Matthew R. Francis

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

fō-ˈtä-nik 

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

But in the void of space, even the tiny kick of a photon becomes a powerful engine. —Mrigakshi Dixit, Interesting Engineering, 9 Apr. 2026

The Scripps Research team used minimal fluorescence photon flux super-resolution microscopy to explore the difference between the two proteins. —Noah Lyons, San Diego Union-Tribune, 9 Apr. 2026

And of course, the foremost reason is nobody could image into the brain before, until photon microscopy became available. —Amanda Erickson, STAT, 7 Apr. 2026

If a photon and the OMG particle had been in a race since the universe first formed, the particle now would only be about 600 meters behind. —Phil Plait, Scientific American, 3 Apr. 2026

Word History

Etymology

phot- + -on entry 2

First Known Use

1916, in the meaning defined at sense 2

Rhymes for photon

• anton
• argon
• axon
• baronne
• baryon
• baton
• boron
• buisson
• bygone
• capon
• cardon
• chiffon

Kids Definition

photon

noun

pho·​ton ˈfō-ˌtän 

: a tiny particle or bundle of electromagnetic radiation

Medical Definition

photon

noun

pho·​ton ˈfō-ˌtän 

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