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
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: 1916
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
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