Electromagnetic radiation (EMR).
Radiant energy, such as light or radio waves, which consists of photons.
Photons are elementary subatomic particles (particles smaller than an atom not known to consist of any subparticles) which travel through space at the speed of light - 300 000 km/sec or 186 000 miles/sec in a vacuum. Although they’re actually particles they nonetheless behave like waves in many circumstances; a counter-intuitive fact which had early researchers highly confused.
All EMR consists of photons - the differences between the various types of EMR stem simply from the amount of energy they carry, which is related to the wavelength of the radiation. Short wavelengths carry high levels of energy and long wavelengths carry low levels of energy.
From high energy to low, EMR consists of gamma radiation, X-rays, ultraviolet radiation, light, infrared energy, microwave radiation and radio waves. These seemingly disparate forms of energy are all electromagnetic radiation.
The visible light spectrum is the most important form of EMR to our daily lives since it’s the only kind which most humans can detect unassisted. Light consists of EMR which varies from 400 to 700 nanometres or so. The specific wavelength determines what we sense as colour information. Ultraviolet radiation (below the 400nm end of light) and infrared (above the 700nm end of light) are other types of photographically useful EMR.
cf. infrared, light, nm, ultraviolet, X-rays.
Entry last updated 2002-04-27. Term 412 of 1487.
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