page_title: Electromagnetic radiation
section_title: Electromagnetic spectrum
hierarchical_section_title: Electromagnetic radiation / Electromagnetic spectrum
context_page_description: In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays.
  Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The wavefront of electromagnetic waves emitted from a point source is a sphere. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter.
context_section_description: EM radiation (the designation 'radiation' excludes static electric and magnetic and near fields) is classified by wavelength into radio, microwave, infrared, visible, ultraviolet, X-rays and gamma rays. Arbitrary electromagnetic waves can be expressed by Fourier analysis in terms of sinusoidal monochromatic waves, which in turn can each be classified into these regions of the EMR spectrum.
  For certain classes of EM waves, the waveform is most usefully treated as random, and then spectral analysis must be done by slightly different mathematical techniques appropriate to random or stochastic processes. In such cases, the individual frequency components are represented in terms of their power content, and the phase information is not preserved. Such a representation is called the power spectral density of the random process. Random electromagnetic radiation requiring this kind of analysis is, for example, encountered in the interior of stars, and in certain other very wideband forms of radiation such as the Zero point wave field of the electromagnetic vacuum.
  The behavior of EM radiation and its interaction with matter depends on its frequency, and changes qualitatively as the frequency changes. Lower frequencies have longer wavelengths, and higher frequencies have shorter wavelengths, and are associated with photons of higher energy. There is no fundamental limit known to these wavelengths or energies, at either end of the spectrum, although photons with energies near the Planck energy or exceeding it (far too high to have ever been observed) will require new physical theories to describe.
caption: Legend:
   γ = Gamma rays
   
   HX = Hard X-rays
   SX = Soft X-Rays
   
   EUV = Extreme-ultraviolet
   NUV = Near-ultraviolet
   
   Visible light (colored bands)
   
   NIR = Near-infrared
   MIR = Mid-infrared
   FIR = Far-infrared
   
   EHF = Extremely high frequency (microwaves)
   SHF = Super-high frequency (microwaves)
   
   UHF = Ultrahigh frequency (radio waves)
   VHF = Very high frequency (radio)
   HF = High frequency (radio)
   MF = Medium frequency (radio)
   LF = Low frequency (radio)
   VLF = Very low frequency (radio)
   VF = Voice frequency
   ULF = Ultra-low frequency (radio)
   SLF = Super-low frequency (radio)
   ELF = Extremely low frequency (radio)