Radiant energy

Radiant energy is the energy of electromagnetic waves, or sometimes of other forms of radiation. The quantity of radiant energy may be calculated by integrating radiant flux (or power) with respect to time and, like all forms of energy, its SI unit is the joule. The term is used particularly when radiation is emitted by a source into the surrounding environment.

Terminology use and history
The term "radiant energy" is most commonly used in the fields of radiometry, solar energy, heating and lighting, but is also sometimes used in other fields (such as telecommunications). Radiant energy may or may not affect the eye and produce vision. In modern applications involving transmission of power from one location to another, "radiant energy" is sometimes used to refer to the electromagnetic waves themselves, rather than their energy (a property of the waves). In the past, the term "electro-radiant energy" has also been used.

Historically, the propagation of electromagnetic radiation was presumed to rely on a medium filling all space, known as the aether. Electromagnetic waves were presumed to propagate through this medium by inducing transverse electric and magnetic stresses and strains, analogous to those induced by shear waves propagating through a physical medium. In modern times, the propagation of electromagnetic waves has been shown not to require any physical medium, although some interpretations of general relativity can be viewed as implying that space acts as a kind of non-physical "medium" for light.

Analysis
Because electromagnetic (EM) radiation can be conceptualized as a stream of photons, radiant energy can be viewed as the energy carried by these photons. Alternatively, EM radiation can be viewed as an electromagnetic wave, which carries energy in its oscillating electric and magnetic fields. These two views are completely equivalent and are reconciled to one another in quantum field theory (see wave-particle duality).

EM radiation can have various frequencies. The bands of frequency present in a given EM signal may be sharply defined, as is seen in atomic spectra, or may be broad, as in blackbody radiation. In the photon picture, the energy carried by each photon is proportional to its frequency. In the wave picture, the energy of a monochromatic wave is proportional to its intensity. This implies that if two EM waves have the same intensity, but different frequencies, the one with the higher frequency "contains" fewer photons, since each photon is more energetic.

When EM waves are absorbed by an object, the energy of the waves is typically converted to heat. This is a very familiar effect, since sunlight warms surfaces that it irradiates. Often this phenomenon is associated particularly with infrared radiation, but any kind of electromagnetic radiation will warm an object that absorbs it. EM waves can also be reflected or scattered, in which case their energy is redirected or redistributed as well.

Open systems
Radiant energy is one of the mechanisms by which energy can enter or leave an open system. Such a system can be man-made, such as a solar energy collector, or natural, such as the Earth's atmosphere. In geophysics, transparent greenhouse gases trap the sun's radiant energy (at certain wavelengths), allowing it to penetrate deep into the atmosphere or all the way to the Earth's surface, where they are re-emitted as longer wavelength radiation (chiefly infrared radiation). Radiant energy is produced in the sun as a result of nuclear fusion.

Applications
Radiant energy, as well as convective energy and conductive energy, is used for radiant heating. It can be generated electrically by infrared lamps, or can be absorbed from sunlight and used to heat water. The heat energy is emitted from a warm element (floor, wall, overhead panel) and warms people and other objects in rooms rather than directly heating the air. The internal air temperature for radiant heated buildings may be lower than for a conventionally heated building to achieve the same level of body comfort (the perceived temperature is actually the same).

Various other applications of radiant energy have been devised. These include: Many of these applications involve a source of radiant energy and a detector that responds to that radiation and provides a signal representing some characteristic of the radiation. Radiant energy detectors produce responses to incident radiant energy either as an increase or decrease in electric potential or current flow or some other perceivable change, such as exposure of photographic film.
 * Treatment and inspection
 * Separating and sorting
 * Medium of control
 * Medium of communication

One of the earliest wireless telephones to be based on radiant energy was invented by Nikola Tesla. The device used transmitters and receivers whose resonances were tuned to the same frequency, allowing communication between them. In 1916, he recounted an experiment he had done in 1896. He recalled that "Whenever I received the effects of a transmitter, one of the simplest ways [to detect the wireless transmissions] was to apply a magnetic field to currents generated in a conductor, and when I did so, the low frequency gave audible notes."

General Information

 * Patents > Guidance, Tools, and Manuals >> Classification >>> Class Definition : Class 250, Radiant Energy, USPTO. March 2006.
 * Finke, R. C., "Direct conversion of infrared radiant energy for space power applications". In R and D Associates Proc. of the AFOSR Spec. Conf. on Prime-Power for High Energy Space Systems, Vol. 2 22 p (SEE N83-15860 06-44). 1982.
 * Lang, K. R. (1999). Astrophysical formulae. Astronomy and astrophysics library. Berlin: Springer.
 * Whittaker, E. T. (1910). A history of the theories of aether and electricity from the age of Descartes to the close of the nineteenth century. Dublin University Press series. London: Longmans, Green and Company.
 * Caverly, Donald Philip, "Primer of electronics and radiant energy" New York, McGraw-Hill, 1952.
 * Hardis, Jonathan E., "Visibility of Radiant Energy". PDF.
 * Lighting Design Knowledgebase
 * Sir Joseph Larmor, Aether and Matter: A Development of the Dynamical Relations of the Aether to Material Systems on the Basis of the Atomic Constitution of Matter. University press, 1900. 365 pages.
 * Philosophical magazine. (1798). London: Taylor & Francis.
 * Hegeler, E. C., & Carus, P. (1890). The Monist. La Salle, Ill. [etc.]: Published by Open Court for the Hegeler Institute.
 * George Frederick Barker, Physics: Advanced Course. Henry Holt and Company, 1893. 902 pages.
 * Frederick Booth, Radiant Energy and the Ophthalmic Lens. P. Blakiston's Son & Co., 1921. 226 pages.
 * Thomas O'Conor Sloane, Electricity Simplified: The Practice and Theory of Electricity. The N.W. Henley publishing co., 1905. 172 pages.
 * "Hermann von Helmholtz" (Obiturary). Royal Society (Great Britain). (1854). Proceedings of the Royal Society of London. London: Printed by Taylor and Francis.
 * Whittaker, E. T., What Is Energy?. The Mathematical Gazette, 1929.
 * Peter Michael Harman, George Basalla, and Owen Hannaway, "Energy, Force and Matter: The Conceptual Development of Nineteenth-century Physics". Cambridge University Press, 1982.
 * U. Fano, Atomic Theory of Electromagnetic Interactions in Dense Materials. 8 May 1956.
 * JM Dawson, Particle simulation of plasmas. Reviews of Modern Physics, 1983.
 * Glenn R. Elion, Electro-Optics Handbook. CRC Press Technology & Industrial Arts, 1979. ISBN 0824768795
 * Draper, J. W. (1878). Scientific memoirs, being experimental contributions to a knowledge of radiant energy. New York: Harper.

Patents

 * - Transmitting and recording sound by radiant energy - Alexander Graham Bell (Filed May 3, 1884; Issued May 4, 1886.)
 * - Apparatus for the utilization of radiant energy - N. Tesla
 * - Method of utilizing of radiant energy - N. Tesla
 * - Wireless Telegraphy System - Harry Shoemaker (Filed Jan 11, 1902; Issued Sep 30, 1902
 * - Transmitting apparatus - Harry Shoemaker (Filed Jun 17, 1905; Issued Oct 10, 1911)
 * - Signaling by electroradiant energy - C. D. Ehret (Filed Dec 2, 1903)
 * - Method of generating radiant energy and projecting same through free air for producing heat - William M. Meacham (Filed Apr 12, 1915; Issued Oct 7, 1915.)
 * - Radiant energy signalling system case - Theodore Case (Filed Jan 22, 1918; Issued May 24, 1921.)20, 1925.)
 * - System for control of moving bodies by radiant energy - John Hays Hammond Jr. (Filed Aug 6, 1914; Issued Jun 6, 1922)
 * - Transmission system for radiant energy - John Hays Hammond Jr. (Filed Jun 22, 1917; Issued Aug 15, 1922)
 * - Marine trailer for radiant energy receiving systems - John Hays Hammond Jr. (Filed Dec 23, 1918; Issued Aug 1, 1922)
 * - Perception of radiant energy - E. Benson (Filed Apr 13, 1918; Issued Jan
 * - Radio apparatus - Arthur Atwater Kent (Filed Nov 29, 1922; Issued Aug 31, 1926.)
 * - Electromagnetic horn - W. L. Barrow (Filed Sep 19, 1938; Issued Oct 13, 1942)
 * - Radiant energy receiver - Gilbert C. Larson (Filed Sep 20, 1943; Issued Sep 10, 1846.)
 * - Method of generating electricity from radiant energy called variable polarizability capacity generator - L. R. O'Hare
 * - Energy conversion systems - Paulo N. Correa and Alexandra N. Correa (Filed Oct 15, 2002; Issued May 30, 2006)

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