Definition of photon
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
photonicplay \fō-ˈtä-nik\ adjective
Recent Examples of photon from the Web
Sunlight is composed of packets of energy called photons.
Well the $9 billion photon-smashing invention encased in a 17-mile tunnel fired up in 2008.
A giant solar collector – 5 micrometers thick and 3 miles long on a side – captures the kinetic energy of photons in sunlight, carrying the ship through the inner solar system like an America's Cup yacht.
These example sentences are selected automatically from various online news sources to reflect current usage of the word 'photon'. Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
Did You Know?
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.
Origin and Etymology of photon
phot- + 2-on
First Known Use: 1916See Words from the same year
PHOTON Defined for English Language Learners
Definition of photon for English Language Learners
physics : a tiny particle of light or electromagnetic radiation
Medical Definition of photon
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
Seen and Heard
What made you want to look up photon? Please tell us where you read or heard it (including the quote, if possible).