photon

noun

pho·​ton ˈfō-ˌtän 

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

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

None of these things are fully appropriate because a photon has no exact intuitive analog. —Big Think, 29 Oct. 2025

Projects such as the Axion Dark Matter Experiment, a collaboration of the University of Washington, Lawrence Livermore National Laboratory and other institutions, are currently hunting these particles by using intense magnetic fields to convert them to detectable microwave photons. —Stephanie Pappas, Scientific American, 27 Oct. 2025

But once the infrastructure is in place, gusts and photons are free. —Joan Meiners, AZCentral.com, 27 Oct. 2025

According to certain segments of the wellness crowd, this is tantamount to taking a shvitz in Chernobyl, because the light emitted by modern devices is mostly in the blue range of the spectrum, and the photoreceptors regulating our circadian rhythms are particularly attuned to blue photons. —Rowan Jacobsen, Harpers Magazine, 24 Oct. 2025

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