photon

noun

pho·​ton ˈfō-ˌtän 

1

: a quantum of electromagnetic radiation

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

Did you know?

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

Lunar horizon glow occurs when photons from the sun react with the moon’s soil, or regolith, causing electrostatic particles to float. —Jackie Wattles, CNN, 15 Jan. 2025

Like qubits, photons can be entangled—connected in a uniquely quantum way that’s useful for computation—by passing them through devices such as resonators and phase shifters. —IEEE Spectrum, 9 Jan. 2025

In principle, any quantum mechanical system—atoms, molecules, ions, photons—could be fashioned into a qubit. —Charina Chou, Foreign Affairs, 7 Jan. 2025

Instead, most of the influence matter has had on these photons comes from materials inside a galaxy—either the galaxy that hosts the source or within our own Milky Way. —John Timmer, Ars Technica, 3 Jan. 2025

Word History

Etymology

phot- + -on entry 2

First Known Use

1916, in the meaning defined at sense 2

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