What does photon mean?
A photon is the smallest discrete unit of electromagnetic radiation. Light, radio waves, gamma rays, and other forms of electromagnetic radiation can be described as streams of photons. The word is especially important in quantum physics, where electromagnetic radiation is treated not only as a wave but also as a stream of particles. A photon's energy depends on the frequency of the radiation: higher-frequency radiation, such as ultraviolet or gamma rays, consists of more energetic photons than lower-frequency radio waves. Photons are electrically neutral, travel at the speed of light in vacuum, and are commonly detected by converting their energy into an electrical signal. The term is distinct from a proton or a neutron and should not be confused with a phonon, which is a quantum of vibration in a material.
nounA photon is the smallest discrete quantity of electromagnetic radiation, regarded in quantum physics as a particle that carries light or other electromagnetic energy.
- A photon is the quantum or smallest indivisible unit of electromagnetic radiation, such as visible light, ultraviolet radiation, or gamma rays. In modern physics, it is the particle carrier of electromagnetic energy.
"The detector recorded a single photon after the light passed through the filter."
"The instrument was sensitive enough to detect individual photons."
"Photons from the distant star were converted into electrical signals by the telescope."
The plural is formed by adding -s: one photon, two photons.
"The researchers measured the photons emitted by the material."
Every ray of light is made of countless photons, tiny particles that travel at the speed of light.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does photon come from?
The word photon was formed in the early 20th century from Greek phōs, meaning “light,” and the scientific suffix -on. It was introduced in the development of quantum theory to name the particle associated with electromagnetic radiation. Its relatives in English, including photography, photosynthesis, and photometry, share the same Greek element referring to light.
Related word forms
How photon is actually used
The term is primarily technical and is used in physics and astronomy. In general scientific communication, it usually refers specifically to a particle of electromagnetic radiation, rather than to light in its broader sense.
Easily confused with photon
A photon is a quantum of electromagnetic radiation, whereas a phonon is a quantum of vibrational energy in a material.
A photon is an electrically neutral particle of electromagnetic radiation, whereas a proton is a positively charged subatomic particle.