A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
White light is dispersed by a prism into the colors of the visible spectrum.
The electromagnetic spectrum, with the visible portion highlighted
Shows the relative wavelengths of the electromagnetic waves of three different colours of light (blue, green, and red) with a distance scale in micrometers along the x-axis.
Laser beams with visible spectrum
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power, so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Electromagnetic radiation thus includes the far field part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, forms part of the changing electromagnetic field, but does not count as electromagnetic radiation.
Newton's color circle, from Opticks of 1704, showing the colors he associated with musical notes. The spectral colors from red to violet are divided by the notes of the musical scale, starting at D. The circle completes a full octave, from D to D. Newton's circle places red, at one end of the spectrum, next to violet, at the other. This reflects the fact that non-spectral purple colors are observed when red and violet light are mixed.
Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily
Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. The electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together.
Newton's observation of prismatic colors (David Brewster 1855)
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.
Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation.
How visible light interacts with objects to make them colorful
Hong Kong illuminated by colourful artificial lighting.
James Clerk Maxwell
Approximation of spectral colors on a display results in somewhat distorted chromaticity
Pierre Gassendi.
Electromagnetic spectrum with visible light highlighted
Earth's atmosphere partially or totally blocks some wavelengths of electromagnetic radiation, but in visible light it is mostly transparent
Christiaan Huygens.
Rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation
Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.

Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye.

- Light

It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

- Electromagnetic radiation

Electromagnetic radiation in this range of wavelengths is called visible light or simply light.

- Visible spectrum

Generally, electromagnetic radiation (EMR) is classified by wavelength into radio waves, microwaves, infrared, the visible spectrum that we perceive as light, ultraviolet, X-rays and gamma rays.

- Light

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.

- Electromagnetic radiation
A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.

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The electromagnetic spectrum

Electromagnetic spectrum

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The electromagnetic spectrum
A diagram of the electromagnetic spectrum, showing various properties across the range of frequencies and wavelengths
Plot of Earth's atmospheric opacity to various wavelengths of electromagnetic radiation. This is the surface-to-space opacity, the atmosphere is transparent to longwave radio transmissions within the troposphere but opaque to space due to the ionosphere.
Plot of atmospheric opacity for terrestrial to terrestrial transmission showing the molecules responsible for some of the resonances
The amount of penetration of UV relative to altitude in Earth's ozone

The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.

This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end.

The wavelength of UV rays is shorter than the violet end of the visible spectrum but longer than the X-ray.

A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) radiation.


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A pseudocolor image of two people taken in long-wavelength infrared (body-temperature thermal) radiation.
This false-color infrared space telescope image has blue, green and red corresponding to 3.4, 4.6, and 12 μm wavelengths, respectively.
Plot of atmospheric transmittance in part of the infrared region
Materials with higher emissivity appear closer to their true temperature than materials that reflect more of their different-temperature surroundings. In this thermal image, the more reflective ceramic cylinder, reflecting the cooler surroundings, appears to be colder than its cubic container (made of more emissive silicon carbide), while in fact, they have the same temperature.
Active-infrared night vision: the camera illuminates the scene at infrared wavelengths invisible to the human eye. Despite a dark back-lit scene, active-infrared night vision delivers identifying details, as seen on the display monitor.
Thermography helped to determine the temperature profile of the Space Shuttle thermal protection system during re-entry.
Hyperspectral thermal infrared emission measurement, an outdoor scan in winter conditions, ambient temperature −15 °C, image produced with a Specim LWIR hyperspectral imager. Relative radiance spectra from various targets in the image are shown with arrows. The infrared spectra of the different objects such as the watch clasp have clearly distinctive characteristics. The contrast level indicates the temperature of the object.
Infrared light from the LED of a remote control as recorded by a digital camera
Reflected light photograph in various infrared spectra to illustrate the appearance as the wavelength of light changes.
Infrared hair dryer for hair salons, c. 2010s
IR satellite picture of cumulonimbus clouds over the Great Plains of the United States.
The greenhouse effect with molecules of methane, water, and carbon dioxide re-radiating solar heat
Beta Pictoris with its planet Beta Pictoris b, the light-blue dot off-center, as seen in infrared. It combines two images, the inner disc is at 3.6 μm.
An infrared reflectogram of Mona Lisa by Leonardo da Vinci
Thermographic image of a snake eating a mouse
Infrared radiation was discovered in 1800 by William Herschel.
Infrared hair dryer for hair salons, c. 2010s

Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light.

IR is generally understood to encompass wavelengths from around 1 millimeter (300 GHz) to the nominal red edge of the visible spectrum, around 700 nanometers (430 THz).

The wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown.


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Spatial period of a periodic wave—the distance over which the wave's shape repeats.

Spatial period of a periodic wave—the distance over which the wave's shape repeats.

The wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests (on top), or troughs (on bottom), or corresponding zero crossings as shown.
Sinusoidal standing waves in a box that constrains the end points to be nodes will have an integer number of half wavelengths fitting in the box.
A standing wave (black) depicted as the sum of two propagating waves traveling in opposite directions (red and blue)
Wavelength is decreased in a medium with slower propagation.
Refraction: upon entering a medium where its speed is lower, the wave changes direction.
Separation of colors by a prism (click for animation)
Various local wavelengths on a crest-to-crest basis in an ocean wave approaching shore
A sinusoidal wave travelling in a nonuniform medium, with loss
A wave on a line of atoms can be interpreted according to a variety of wavelengths.
Near-periodic waves over shallow water
Wavelength of a periodic but non-sinusoidal waveform.
A propagating wave packet
Pattern of light intensity on a screen for light passing through two slits. The labels on the right refer to the difference of the path lengths from the two slits, which are idealized here as point sources.
Diffraction pattern of a double slit has a single-slit envelope.
Relationship between wavelength, angular wavelength, and other wave properties.

Examples of waves are sound waves, light, water waves and periodic electrical signals in a conductor.

A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary.

The name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum.