Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The quantum of electromagnetic energy, regarded as a discrete particle having zero mass, no electric charge, and an indefinitely long lifetime. See Table at subatomic particle.
  • n. A unit of retinal illumination, equal to the amount of light that reaches the retina through 1 square millimeter of pupil area from a surface having a brightness of 1 candela per square meter.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The quantum of light and other electromagnetic energy, regarded as a discrete particle having zero rest mass, no electric charge, and an indefinitely long lifetime. It is a gauge boson.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a quantum of electromagnetic radiation; an elementary particle that is its own antiparticle

Etymologies

From photo- + -on. (Wiktionary)

Examples

Comments

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  • "The modern photon concept was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. It also accounted for anomalous observations, including the properties of black body radiation, that other physicists, most notably Max Planck, had sought to explain using semiclassical models, in which light is still described by Maxwell's equations, but the material objects that emit and absorb light, do so in amounts of energy that are quantized (i.e., they change energy only by certain particular discrete amounts and cannot change energy in any arbitrary way). Although these semiclassical models contributed to the development of quantum mechanics, many further experiments starting with Compton scattering of single photons by electrons, first observed in 1923, validated Einstein's hypothesis that light itself is quantized. In 1926 the chemist Gilbert N. Lewis coined the name photon for these particles, and after 1927, when Arthur H. Compton won the Nobel Prize for his scattering studies, most scientists accepted the validity that quanta of light have an independent existence, and Lewis' term photon for light quanta was accepted."

    --Wikipedia (http://en.wikipedia.org/w/index.php?title=Photon&oldid=509270454)

    August 27, 2012