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

Detecting cosmic ghosts Neutrinos are the second-most prevalent particles in the entire universe besides photons, particles of light. — Robert Lea, Space.com, 6 Oct. 2026

In a smaller number of these interactions, a photon may not break apart the nucleus but strike only a nucleon, generating no ‘forward’ neutrons. — Ameya Paleja, Interesting Engineering, 2 Oct. 2026

When a photon strikes one of these complexes, its electromagnetic energy is absorbed and boosts an electron in the complex into an excited state. — Elise Cutts, Quanta Magazine, 23 Sep. 2026

To store a qubit's state, the qubit transfers the information to a resonator, a container that traps a wave, where it's held as either zero or one microwave photon bouncing back and forth until the qubit takes it back. — New Atlas, 23 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