The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 380 to 740 nanometers. In terms of frequency, this corresponds to a band in the vicinity of 430–770 THz.
The spectrum does not contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations like magenta, for example, are absent because they can only be made from a mix of multiple wavelengths. Colors containing only one wavelength are also called pure colors or spectral colors.
Visible wavelengths pass largely unattenuated through the Earth's atmosphere via the "optical window" region of the electromagnetic spectrum. An example of this phenomenon is when clean air scatters blue light more than red light, and so the midday sky appears blue. The optical window is also referred to as the "visible window" because it overlaps the human visible response spectrum. The near infrared (NIR) window lies just out of the human vision, as well as the medium wavelength infrared (MWIR) window, and the long wavelength or far infrared (LWIR or FIR) window, although other animals may experience them.
In the 17th century, Isaac Newton discovered that prisms could disassemble and reassemble white light, and described the phenomenon in his book Opticks. He was the first to use the word spectrum (Latin for "appearance" or "apparition") in this sense in print in 1671 in describing his experiments in optics. Newton observed that, when a narrow beam of sunlight strikes the face of a glass prism at an angle, some is reflected and some of the beam passes into and through the glass, emerging as different-colored bands. Newton hypothesized light to be made up of "corpuscles" (particles) of different colors, with the different colors of light moving at different speeds in transparent matter, red light moving more quickly than violet in glass. The result is that red light is bent (refracted) less sharply than violet as it passes through the prism, creating a spectrum of colors.
Newton originally divided the spectrum into six named colors: red, orange, yellow, green, blue, and violet. He later added indigo as the seventh color since he believed that seven was a perfect number as derived from the ancient Greek sophists, of there being a connection between the colors, the musical notes, the known objects in the solar system, and the days of the week. The human eye is relatively insensitive to indigo's frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some later commentators, including Isaac Asimov, have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet. However, the evidence indicates that what Newton meant by "indigo" and "blue" does not correspond to the modern meanings of those color words. Comparing Newton's observation of prismatic colors to a color image of the visible light spectrum shows that "indigo" corresponds to what is today called blue, whereas "blue" corresponds to cyan.
In the 18th century, Goethe wrote about optical spectra in his Theory of Colours. Goethe used the word spectrum (Spektrum) to designate a ghostly optical afterimage, as did Schopenhauer in On Vision and Colors. Goethe argued that the continuous spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow and blue-cyan edges with white between them. The spectrum appears only when these edges are close enough to overlap.
In the early 19th century, the concept of the visible spectrum became more definite, as light outside the visible range was discovered and characterized by William Herschel (infrared) and Johann Wilhelm Ritter (ultraviolet), Thomas Young, Thomas Johann Seebeck, and others. Young was the first to measure the wavelengths of different colors of light, in 1802.
The connection between the visible spectrum and color vision was explored by Thomas Young and Hermann von Helmholtz in the early 19th century. Their theory of color vision correctly proposed that the eye uses three distinct receptors to perceive color.
Many species can see light within frequencies outside the human "visible spectrum". Bees and many other insects can detect ultraviolet light, which helps them find nectar in flowers. Plant species that depend on insect pollination may owe reproductive success to their appearance in ultraviolet light rather than how colorful they appear to humans. Birds, too, can see into the ultraviolet (300–400 nm), and some have sex-dependent markings on their plumage that are visible only in the ultraviolet range. Many animals that can see into the ultraviolet range, however, cannot see red light or any other reddish wavelengths. Bees' visible spectrum ends at about 590 nm, just before the orange wavelengths start. Birds, however, can see some red wavelengths, although not as far into the light spectrum as humans. The popular belief that the common goldfish is the only animal that can see both infrared and ultraviolet light  is incorrect, because goldfish cannot see infrared light. Similarly, dogs are often thought to be color blind but they have been shown to be sensitive to colors, though not as many as humans. Some snakes can "see" radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the prey at which it strikes, and other snakes with the organ may detect warm bodies from a meter away. It may also be used in thermoregulation and predator detection. (See Infrared sensing in snakes)
|Violet||380–450 nm||680–790 THz||2.95–3.10 eV|
|Blue||450–485 nm||620–680 THz||2.64–2.75 eV|
|Cyan||485–500 nm||600–620 THz||2.48–2.52 eV|
|Green||500–565 nm||530–600 THz||2.25–2.34 eV|
|Yellow||565–590 nm||510–530 THz||2.10–2.17 eV|
|Orange||590–625 nm||480–510 THz||2.00–2.10 eV|
|Red||625–740 nm||405–480 THz||1.65–2.00 eV|
Colors that can be produced by visible light of a narrow band of wavelengths (monochromatic light) are called pure spectral colors. The various color ranges indicated in the illustration are an approximation: The spectrum is continuous, with no clear boundaries between one color and the next.
Color displays (e.g. computer monitors and televisions) cannot reproduce all colors discernible by a human eye. Colors outside the color gamut of the device, such as most spectral colors, can only be approximated. For color-accurate reproduction, a spectrum can be projected onto a uniform gray field. The resulting mixed colors can have all their R, G, B coordinates non-negative, and so can be reproduced without distortion. This accurately simulates looking at a spectrum on a gray background.
Spectroscopy is the study of objects based on the spectrum of color they emit, absorb or reflect. Spectroscopy is an important investigative tool in astronomy, where scientists use it to analyze the properties of distant objects. Typically, astronomical spectroscopy uses high-dispersion diffraction gratings to observe spectra at very high spectral resolutions. Helium was first detected by analysis of the spectrum of the sun. Chemical elements can be detected in astronomical objects by emission lines and absorption lines.
Anthocyanidins are common plant pigments. They are the sugar-free counterparts of anthocyanins based on the flavylium ion or 2-phenylchromenylium, which is a type of oxonium ion (chromenylium is referred also to as benzopyrylium). They form a large group of polymethine dye. In particular anthocyanidins are salt derivatives of the 2-phenylchromenylium cation, also known as flavylium cation. As shown in the figure below, the phenyl group at the 2-position can carry different substituents. The counterion of the flavylium cation is mostly chloride. With this positive charge, the anthocyanidins differ from other flavonoids.
31 monomeric anthocyanidins have been properly identified, most of the anthocyanins are based on cyanidin (30%), delphinidin (22%), and pelargonidin (18%), respectively. Altogether 20% of the anthocyanins are based on the three common anthocyanidins (peonidin, malvidin, and petunidin) that are methylated. Around 3, 3, and 2% of the anthocyanins or anthocyanidins are labeled as 3-desoxyanthocyanidins, rare methylatedanthocyanidins, and 6-hydroxyanthocyanidins, respectively.
In bryophytes, anthocyanins are usually based on 3-desoxyanthocyanidins located in the cell wall. A new anthocyanidin, riccionidin A, has been isolated from the liverwort Ricciocarpos natans. It could be derived from 6,7,2′, 4′, 6′-pentahydroxyflavylium, having undergone ring closure of the 6’ -hydroxyl at the 3-position. Its visible spectrum in methanolic HCl is at 494 nm. This pigment was accompanied by riccionidin B, which most probably is based on two molecules of riccionidin A linked via the 3′- or 5′ -positions. Both pigments were also detected in the liverworts Marchantia polymorpha, Riccia duplex, and Scapania undulata.Blue ice (glacial)
Blue ice occurs when snow falls on a glacier, is compressed, and becomes part of the glacier. Air bubbles are squeezed out and ice crystals enlarge, making the ice appear blue.
Small amounts of regular ice appear to be white because of air bubbles inside them and also because small quantities of water appear to be colourless. In glaciers, the pressure causes the air bubbles to be squeezed out, increasing the density of the created ice. Large quantities of water appear to be blue, as it absorbs other colours more efficiently than blue. A large piece of compressed ice, or a glacier, similarly appears blue.
The blue color is sometimes wrongly attributed to Rayleigh scattering, which is responsible for the color of the sky. Rather, water ice is blue for the same reason that large quantities of liquid water are blue: it is a result of an overtone of an oxygen–hydrogen (O−H) bond stretch in water, which absorbs light at the red end of the visible spectrum. In the case of oceans or lakes, some of the light hitting the surface of water is reflected back directly, but most of it penetrates the surface, interacting with its molecules. The water molecule can vibrate in different modes when light hits it. The red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light is composed of the shorter wavelengths of blue and violet. This is the main reason why the ocean is blue. So, water owes its intrinsic blueness to selective absorption in the red part of its visible spectrum. The absorbed photons promote transitions to high overtone and combination states of the nuclear motions of the molecule, i.e. to highly excited vibrations.
An example of blue ice was observed in Tasman Glacier, New Zealand in January 2011.Brownian noise
In science, Brownian noise (Sample ), also known as Brown noise or red noise, is the kind of signal noise produced by Brownian motion, hence its alternative name of random walk noise. The term "Brown noise" does not come from the color, but after Robert Brown, the discoverer of Brownian motion. The term "red noise" comes from the "white noise"/"white light" analogy; red noise is strong in longer wavelengths, similar to the red end of the visible spectrum.Chromophore
A chromophore is the part of a molecule responsible for its color.
The color that is seen by our eyes is the one not absorbed within a certain wavelength spectrum of visible light. The chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.
In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change of the molecule when hit by light.DS-P1-Yu
DS-P1-Yu was a series of Soviet satellites developed by the Yuzhnoye Design Office of Ukraine, for use in calibrating the Dnestr space surveillance and early-warning radar system. Between 1964 and 1976, a total of 79 satellites were launched on Kosmos launchers, with seven failing to reach orbit.The dodecahedral satellites had a mass of 193–240 kilograms (425–529 lb) and an operational lifetime of 60 days. They were covered in solar panels and a metallic mesh transparent to visible spectrum light and opaque to radio frequencies.The DS-P1-Yu replaced the similar DS-P1, of which four were launched between 1962 and 1964, with one failure to reach orbit.F-center
An F-center, Farbe center or color center (from the original German Farbzentrum; Farbe means color, and zentrum center) is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more unpaired electrons. Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually transparent becomes colored. This is used to identify many compounds, especially zinc oxide (yellow).Geometric albedo
In astronomy, the geometric albedo of a celestial body is the ratio of its actual brightness as seen from the light source (i.e. at zero phase angle) to that of an idealized flat, fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. (This phase angle refers to the direction of the light paths and is not a phase angle in its normal meaning in optics or electronics.)
Diffuse scattering implies that radiation is reflected isotropically with no memory of the location of the incident light source. Zero phase angle corresponds to looking along the direction of illumination. For Earth-bound observers this occurs when the body in question is at opposition and on the ecliptic.
The visual geometric albedo refers to the geometric albedo quantity when accounting for only electromagnetic radiation in the visible spectrum.Helium–neon laser
A helium–neon laser or HeNe laser, is a type of gas laser whose gain medium consists of a mixture of 75% helium and 25% neon at a total pressure of about 1 mm of Hg inside of a small electrical discharge. The best-known and most widely used HeNe laser operates at a wavelength of 632.8 nm, in the red part of the visible spectrum.Luminous energy
In photometry, luminous energy is the perceived energy of light. This is sometimes called the quantity of light. Luminous energy is not the same as radiant energy, the corresponding objective physical quantity. This is because the human eye can only see light in the visible spectrum and has different sensitivities to light of different wavelengths within the spectrum. When adapted for bright conditions (photopic vision), the eye is most sensitive to light at a wavelength of 555 nm. Light with a given amount of radiant energy will have more luminous energy if the wavelength is 555 nm than if the wavelength is longer or shorter. Light whose wavelength is well outside the visible spectrum has a luminous energy of zero, regardless of the amount of radiant energy present.
The SI unit of luminous energy is the lumen second, which is unofficially known as the talbot in honor of William Henry Fox Talbot. In other systems of units, luminous energy may be expressed in basic units of energy.Multi-spectral camouflage
Multi-spectral camouflage is the use of counter-surveillance techniques to conceal objects from detection across several parts of the electromagnetic spectrum at the same time. While traditional military camouflage attempts to hide an object in the visible spectrum, multi-spectral camouflage also tries to simultaneously hide objects from detection methods such as infrared, radar, and millimetre-wave radar imaging.Among animals, both insects such as the eyed hawk-moth, and vertebrates such as tree frogs possess camouflage that works in the infra-red as well as in the visible spectrum.Optical telescope
An optical telescope is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct view, or to make a photograph, or to collect data through electronic image sensors.
There are three primary types of optical telescope:
refractors, which use lenses (dioptrics)
reflectors, which use mirrors (catoptrics)
catadioptric telescopes, which combine lenses and mirrorsA telescope's light gathering power and ability to resolve small detail is directly related to the diameter (or aperture) of its objective (the primary lens or mirror that collects and focuses the light). The larger the objective, the more light the telescope collects and the finer detail it resolves.
People use telescopes and binoculars for activities such as observational astronomy, ornithology, pilotage and reconnaissance, and watching sports or performance arts.Safelight
A safelight is a light source suitable for use in a photographic darkroom. It provides illumination only from parts of the visible spectrum to which the photographic material in use is nearly, or completely, insensitive.Solar telescope
A solar telescope is a special purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, the visible spectrum. Obsolete names for Sun telescopes include heliograph and photoheliograph.Spectral color
A spectral color is a color that is evoked in a normal human by a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths, also known as monochromatic light. Every wavelength of visible light is perceived as a spectral color, in a continuous spectrum; the colors of sufficiently close wavelengths are indistinguishable for the human eye.
The spectrum is often divided into named colors, though any division is somewhat arbitrary; the spectrum is continuous. Traditional colors in English include: red, orange, yellow, green, blue, and violet. In some other languages the ranges corresponding to color names do not necessarily agree with those in English.
The division used by Isaac Newton, in his color wheel, was: red, orange, yellow, green, blue, indigo and violet; a mnemonic for this order is "Roy G. Biv". Less commonly, "VIBGYOR" is also used for the reverse order. In modern divisions of the spectrum, indigo is often omitted.
One needs at least trichromatic color vision for there to be a distinction between spectral and non-spectral colours: trichromacy gives a possibility to perceive both hue and saturation in the chroma. In color models capable of representing spectral colors, such as CIELUV, a spectral color has the maximal saturation.Ultraviolet–visible spectroscopy
Ultraviolet–visible spectroscopy or ultraviolet–visible spectrophotometry (UV–Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible spectral regions. This means it uses light in the visible and adjacent ranges. The absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved. In this region of the electromagnetic spectrum, atoms and molecules undergo electronic transitions. Absorption spectroscopy is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state.V528 Carinae
V528 Carinae (V528 Car, HD 95950, HIP 54021) is a variable star in the constellation Carina.
V528 Carinae has an apparent visual magnitude of +6.75. It is a distant star but the exact distance is uncertain. The Hipparcos satellite gives a negative annual parallax and is not helpful. Its Carina OB2 membership allows the distance to be estimated at 3,850 light-years.V528 Carinae is a red supergiant of spectral type M2 Ib with an effective temperature of 3,700 K. It has a radius of 700 solar radii, making it one of the largest stars. In the visible spectrum luminosity is 11,900 times higher than the sun, but the bolometric luminosity considering all wavelengths reaches 81,000 L☉. It loses mass at 0.5×10−9 M☉ per year.It is classified as a slow irregular variable whose prototype is TZ Cassiopeiae.Wide Field Camera 3
The Wide Field Camera 3 (WFC3) is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum. It was installed as a replacement for the Wide Field and Planetary Camera 2 during the first spacewalk of Space Shuttle mission STS-125 (Hubble Space Telescope Servicing Mission 4) on May 14, 2009.
Radiation (physics and health)