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

Esposito realized the same thing should happen to normal photons. — Matthew Von Hippel, Scientific American, 7 Nov. 2026

When those photons began their journey, modern humans did not exist. — Jamie Carter, Space.com, 6 Nov. 2026

PsiQuantum says its new device can do that without ever having to convert the photons into electrical signals. — Reed Albergotti, semafor.com, 28 Oct. 2026

The numbers were distributed evenly across the incoming beam, and whether the photon passed the polarizer depended on its number and the polarizer’s angle. — Ameya Paleja, Interesting Engineering, 23 Oct. 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