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Meaning & use

photon

noun·Academicphysicstechnical

Last updated

UK/ˈfəʊ.tɒn/
US/ˈfoʊ.tɑːn/

Meanings

  1. nouncountablephysics

    The smallest possible packet of light or other electromagnetic energy, which behaves as a particle with no mass.

    Grammar: Countable: a photon, billions of photons.

    Patterns

    • a photon of light

    A single photon from the lamp can trigger a sensor.

    Plants capture photons from the sun to make food.

    Each photon of blue light carries more energy than one of red light.

  2. nouncountabletechnicalrare

    A unit used in some fields for measuring the brightness of light as seen by the eye.

    Grammar: Rare older usage; modern texts use lumen or lux.

    Older optics textbooks described retinal brightness in photons.

    The measurement was recorded in photons.

Word forms

pluralphotons

Common combinations

emit a photon
An excited atom can emit a photon as it relaxes.
absorb a photon
The molecule absorbs a photon and changes shape.
single photon
Cameras today can detect a single photon.
stream of photons
Light is a stream of photons.
photon energy
Photon energy depends on the light's frequency.

Synonyms and how they differ

light particle
Light particle is a plain-language description, while photon is the exact scientific name.
quantum
Quantum is a broader term for any smallest packet of energy, while a photon is the quantum of light specifically.
ray
A ray describes a beam of light as a line, not as a particle.

Word family

photonic adjective
relating to photons
photonics noun
the science of using light in technology
photoelectric adjective
relating to the release of electrons by light
electron noun
a negatively charged particle

Commonly confused: photon or proton? photon or phonon?

photon vs proton

A proton is a positively charged particle inside an atom, not a particle of light.

photon vs phonon

A phonon is a quantum of vibration, such as sound in a solid, rather than light.

Practice

When light strikes a solar panel, each ___ can knock an electron loose from the material.

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