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

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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

Now in practice, in a realistic experiment, any large system would be very quickly decohered by its, uh, immediate environment, by surrounding photons. — Quanta Magazine, 17 Sep. 2026

The decisive test for Japan’s 600-kilometer network will be whether banks, hospitals, utilities and other customers can use it reliably and economically—not simply whether photons can travel the distance. — John Prisco, Forbes.com, 14 Sep. 2026

The change’s size corresponded to the photon’s energy, which allowed the team to make highly precise measurements. — Georgina Jedikovska, Interesting Engineering, 11 Sep. 2026

The team tested the idea that Lorentz invariance could be violated at high energies, thus changing how photons propagate through space. — Robert Lea, Space.com, 9 Sep. 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