query: What are wavelengths of visible light measured in?

title: Visible spectrum

text: Visible spectrum 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 390 to 700 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

title: Visible spectrum

text: be detected in astronomical objects by emission lines and absorption lines. The shifting of spectral lines can be used to measure the Doppler shift (red shift or blue shift) of distant objects. Visible spectrum 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 390 to 700 nanometers. In terms of frequency, this corresponds to a band in the vicinity of 430–770 THz. The spectrum does not contain all

title: Visible-light astronomy

text: Visible-light astronomy Visible-light astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light (optical telescopes). Visible-light astronomy is part of optical astronomy, and differs from astronomies based on invisible types of light in the electromagnetic radiation spectrum, such as radio waves, infrared waves, ultraviolet waves, X-ray waves and gamma-ray waves. Visible light ranges from 380 to 750 nanometers in wavelength. Visible-light astronomy has existed as long as people have been looking up at the night sky, although it has since improved in its observational capabilities since the invention of the telescope, which

title: Violet light

text: is one of the seven spectral colors described by Isaac Newton in 1672. Violet light is at the higher end of the visible spectrum, with a wavelength ~380-450 nanometers (in experiments, people have so far seen to 310 nm). Light with a shorter wavelength than violet but longer than X-rays and gamma rays is called ultraviolet. Violet objects are normally composed-light violet. Objects reflecting spectral violet appear very dark, because human vision is relatively insensitive to those wavelengths. Monochromatic lamps emitting spectral-violet wavelengths can be roughly approximated by the color named electric violet, which is a composed-light violet producing a

title: Color

text: color in question. The familiar colors of the rainbow in the spectrum—named using the Latin word for "appearance" or "apparition" by Isaac Newton in 1671—include all those colors that can be produced by visible light of a single wavelength only, the "pure spectral" or "monochromatic" colors. The table at right shows approximate frequencies (in terahertz) and wavelengths (in nanometers) for various pure spectral colors. The wavelengths listed are as measured in air or vacuum (see refractive index). The color table should not be interpreted as a definitive list—the pure spectral colors form a continuous spectrum, and how it is divided

title: Visual perception

text: in the visual association cortex that surrounds the striate cortex. The human visual system is generally believed to perceive visible light in the range of wavelengths between 370 and 730 nanometers (0.00000037 to 0.00000073 meters) of the electromagnetic spectrum. However, some research suggests that humans can perceive light in wavelengths down to 340 nanometers (UV-A), especially the young. The major problem in visual perception is that what people see is not simply a translation of retinal stimuli (i.e., the image on the retina). Thus people interested in perception have long struggled to explain what visual processing does to create what

title: High-energy visible light

text: High-energy visible light In ophthalmology, high-energy visible light (HEV light) is high-frequency, high-energy light in the violet/blue band from 400 to 450 nm in the visible spectrum. Despite a lack of concurring scientific evidence, HEV light has sometimes been claimed to be a cause of age-related macular degeneration. Some sunglasses and beauty creams specifically block HEV, for added marketing value. Blue-light hazard is defined as the potential for a photochemically-induced retinal injury resulting from electromagnetic radiation exposure at wavelengths primarily between 400 and This study has not been done in humans, only inconclusively in some rodent, primate, and in vitro

title: Incandescent light bulb

text: ratio of the visible light flux emitted (the "luminous flux") to the total power input to the source, such as a lamp. Visible light is measured in lumens, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light. Not all wavelengths of visible electromagnetic energy are equally effective at stimulating the human eye; the luminous efficacy of radiant energy (LER) is a measure of how well the distribution of energy matches the perception of the eye. The units of luminous efficacy are "lumens per watt" (lpw). The maximum LER possible

title: Visible spectrum

text: 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

title: Ultraviolet–visible spectroscopy

text: single-beam instrument, the cuvette containing only a solvent has to be measured first. Mettler Toledo developed a single beam array spectrophotometer that allows fast and accurate measurements over the UV/VIS range. The light source consists of a Xenon flash lamp for the ultraviolet (UV) as well as for the visible (VIS) and near-infrared wavelength regions covering a spectral range from 190 up to 1100 nm. The lamp flashes are focused on a glass fiber which drives the beam of light onto a cuvette containing the sample solution. The beam passes through the sample and specific wavelengths are absorbed by the

title: Visible spectrum

text: 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

title: Ultraviolet–visible spectroscopy

text: optimal wavelengths for all species involved in equilibria, a reaction can be run to equilibrium, and the concentration of species determined from spectroscopy at various known wavelengths. The equilibrium constant can be calculated as K(eq) = [Products] / [Reactants]. Ultraviolet–visible spectroscopy Ultraviolet–visible spectroscopy or ultraviolet–visible spectrophotometry (UV–Vis or UV/Vis) refers to absorption spectroscopy or reflectance spectroscopy in the ultraviolet-visible spectral region. 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

title: Ultraviolet–visible spectroscopy

text: "reflectance", and is usually expressed as a percentage (%R). The basic parts of a spectrophotometer are a light source, a holder for the sample, a diffraction grating in a monochromator or a prism to separate the different wavelengths of light, and a detector. The radiation source is often a Tungsten filament (300–2500 nm), a deuterium arc lamp, which is continuous over the ultraviolet region (190–400 nm), Xenon arc lamp, which is continuous from 160 to 2,000 nm; or more recently, light emitting diodes (LED) for the visible wavelengths. The detector is typically a photomultiplier tube, a photodiode, a photodiode array

title: Ultraviolet–visible spectroscopy

text: sample components. The remaining light is collected after the cuvette by a glass fiber and driven into a spectrograph. The spectrograph consists of a diffraction grating that separates the light into the different wavelengths, and a CCD sensor to record the data, respectively. The whole spectrum is thus simultaneously measured, allowing for fast recording. Samples for UV/Vis spectrophotometry are most often liquids, although the absorbance of gases and even of solids can also be measured. Samples are typically placed in a transparent cell, known as a cuvette. Cuvettes are typically rectangular in shape, commonly with an internal width of 1

title: Light

text: Light Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10 to 7.00 × 10 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). This wavelength means a frequency range of roughly 430–750 terahertz (THz). The main source of light on Earth is the Sun. Sunlight provides the

title: Visible light imaging

text: of a standardized approach to incorporating visible light images into the electronic medical record Increasingly, visible light imaging is being deployed beyond individual departments, as part of a trend referred to as Enterprise Imaging Including fiberoptic endoscopy and rigid scope endoscopy: Including: General anatomic photography, including: Visible light imaging Visible light imaging is an imaging modality that uses visible light. Even prior to specific support in DICOM for visible light imaging, the standard could already encapsulate color images, e.g., in JPEG format as Secondary Capture images . The need for standardized communication of digital visible light images from various specialties,

title: Visible light imaging

text: Visible light imaging Visible light imaging is an imaging modality that uses visible light. Even prior to specific support in DICOM for visible light imaging, the standard could already encapsulate color images, e.g., in JPEG format as Secondary Capture images . The need for standardized communication of digital visible light images from various specialties, and the need for specialty-specific acquisition context metadata and an appropriate controlled terminology was recognized not long after the DICOM standard was introduced and the terminology of visible light imaging was introduced to the standard The United States Department of Veterans Affairs was an early adopter

title: High-energy visible light

text: studies. The mechanisms for photochemically-induced retinal injury are caused by the absorption of light by photoreceptors in the eye. Under normal conditions when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle. Absorption of blue light, however, has been shown in rats and a susceptible strain of mice to cause a reversal of the process where cells become unbleached and responsive again to light before they are ready. At wavelengths of blue light below 430 nm this greatly increases the potential for oxidative damage. For blue-light circadian

title: Ultraviolet–visible spectroscopy

text: or a charge-coupled device (CCD). Single photodiode detectors and photomultiplier tubes are used with scanning monochromators, which filter the light so that only light of a single wavelength reaches the detector at one time. The scanning monochromator moves the diffraction grating to "step-through" each wavelength so that its intensity may be measured as a function of wavelength. Fixed monochromators are used with CCDs and photodiode arrays. As both of these devices consist of many detectors grouped into one or two dimensional arrays, they are able to collect light of different wavelengths on different pixels or groups of pixels simultaneously. A

title: Visible-light astronomy

text: it is very bright, and can even be seen in daylight. However, Mars, Jupiter, and Saturn can also be seen without the aid of telescopes or binoculars. Constellations and stars are also often observed, and have been used in the past for navigation, especially by ships at sea. One of the most recognizable constellations is the Big Dipper, which is part of the constellation Ursa Major. Constellations also serve to help describe the location of other objects in the sky. Visible-light astronomy Visible-light astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible

title: Visible spectrum

text: 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

title: Visible spectrum

text: used in thermoregulation and predator detection. (See Infrared sensing in snakes) 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

title: Light

text: Generally, EM radiation (the designation "radiation" excludes static electric, magnetic, and near fields), or EMR, is classified by wavelength into radio waves, microwaves, infrared, the visible spectrum that we perceive as light, ultraviolet, X-rays, and gamma rays. The behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. When EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. EMR in the visible light region consists of quanta (called photons) that are at the lower end of the energies that are capable of

title: Ultraviolet–visible spectroscopy

text: dithizonate is a yellow-orange color in diluted solution (1*10^-5 M), and turns blue when subjected with particular wavelengths of visible light (and UV) via a conformational change, but this reaction is reversible back into the yellow "ground state". The rate constant of a particular reaction can be determined by measuring the UV/Vis absorbance spectrum at specific time intervals. Using mercury dithizonate again as an example, one can shine light on the sample to turn the solution blue, then run a UV/Vis test every 10 seconds (variable) to see the levels of absorbed and reflected wavelengths change over time in accordance

title: Visible light communication

text: Visible light communication Visible light communication (VLC) is a data communications variant which uses visible light between 400 and 800 THz (780–375 nm). VLC is a subset of optical wireless communications technologies. The technology uses fluorescent lamps (ordinary lamps, not special communications devices) to transmit signals at 10 kbit/s, or LEDs for up to 500 Mbit/s over short distances. Systems such as RONJA can transmit at full Ethernet speed (10 Mbit/s) over distances of . Specially designed electronic devices generally containing a photodiode receive signals from light sources, although in some cases a cell phone camera or a digital camera

title: Ultraviolet–visible spectroscopy

text: to telescopes to measure the spectra of astronomical features. UV–visible microspectrophotometers consist of a UV–visible microscope integrated with a UV–visible spectrophotometer. A complete spectrum of the absorption at all wavelengths of interest can often be produced directly by a more sophisticated spectrophotometer. In simpler instruments the absorption is determined one wavelength at a time and then compiled into a spectrum by the operator. By removing the concentration dependence, the extinction coefficient (ε) can be determined as a function of wavelength. UV–visible spectroscopy of microscopic samples is done by integrating an optical microscope with UV–visible optics, white light sources, a monochromator,

title: High-energy visible light

text: clinical dermatologic therapies. Constructors such as Philips currently develop devices and techniques emitting in the blue visible spectrum to be used in dermatologic therapy. High-energy visible light In ophthalmology, high-energy visible light (HEV light) is high-frequency, high-energy light in the violet/blue band from 400 to 450 nm in the visible spectrum. Despite a lack of concurring scientific evidence, HEV light has sometimes been claimed to be a cause of age-related macular degeneration. Some sunglasses and beauty creams specifically block HEV, for added marketing value. Blue-light hazard is defined as the potential for a photochemically-induced retinal injury resulting from electromagnetic radiation

title: Visible-light astronomy

text: is commonly credited to Hans Lippershey, a German-Dutch spectacle-maker, although Galileo played a large role in the development and creation of telescopes. Visible-light astronomy continues to advance in the modern day, with projects such as the James Webb Telescope being projected for launch in the next few years. Since visible-light astronomy is restricted to only visible light, no equipment is necessary for simply star gazing. This means that it's the most commonly participated in type of astronomy, as well as the oldest. Before the advent of telescopes, astronomy was limited solely to unaided eyesight. Humans have been looking at stars

title: Visible light communication

text: but cannot perceive the instantaneous color that varies rapidly in time. In other words, CSK transmission maintains a constant time-averaged luminous flux, even as its symbol sequence varies rapidly in chromaticity. Visible light communication Visible light communication (VLC) is a data communications variant which uses visible light between 400 and 800 THz (780–375 nm). VLC is a subset of optical wireless communications technologies. The technology uses fluorescent lamps (ordinary lamps, not special communications devices) to transmit signals at 10 kbit/s, or LEDs for up to 500 Mbit/s over short distances. Systems such as RONJA can transmit at full Ethernet speed

title: Visible-light astronomy

text: and as items of trade. He published his initial telescopic astronomical observations in March 1610 in a brief treatise entitled "Sidereus Nuncius" ("Starry Messenger"). In the modern day, visible-light astronomy is still practiced by many amateur astronomers, especially since telescopes are much more widely available for the public, as compared to when they were first being invented. Government agencies, such as NASA, are very involved in the modern day research and observation of visible objects and celestial bodies. In the modern day, the highest quality pictures and data are obtained via space telescopes; telescopes that are outside of the Earth's

title: Transparency and translucency

text: only certain portions of the visible spectrum. The frequencies of the spectrum which are not absorbed are either reflected back or transmitted for our physical observation. In the visible portion of the spectrum, this is what gives rise to color. Absorption centers are largely responsible for the appearance of specific wavelengths of visible light all around us. Moving from longer (0.7 micrometer) to shorter (0.4 micrometer) wavelengths: red, orange, yellow, green and blue (ROYGB) can all be identified by our senses in the appearance of color by the selective absorption of specific light wave frequencies (or wavelengths). Mechanisms of selective

title: Visible light communication

text: will be sufficient. The image sensor used in these devices is in fact an array of photodiodes (pixels) and in some applications its use may be preferred over a single photodiode. Such a sensor may provide either multi-channel (down to 1 pixel = 1 channel) or a spatial awareness of multiple light sources. VLC can be used as a communications medium for ubiquitous computing and IoT ecosystems because light-producing devices (such as indoor/outdoor lamps, TVs, traffic signs, commercial displays and car headlights/taillights) are used everywhere. Using visible light is also less dangerous for high-power applications because humans can perceive it

title: Light

text: and shrimp) are able to detect ultraviolet, by quantum photon-absorption mechanisms, in much the same chemical way that humans detect visible light. Various sources define visible light as narrowly as 420–680 nm to as broadly as 380–800 nm. Under ideal laboratory conditions, people can see infrared up to at least 1050 nm; children and young adults may perceive ultraviolet wavelengths down to about 310–313 nm. Plant growth is also affected by the color spectrum of light, a process known as photomorphogenesis. The speed of light in a vacuum is defined to be exactly 299,792,458 m/s (approx. 186,282 miles per second).

title: Visible light communication

text: and act to protect their eyes from damage. The history of visible light communications (VLC) dates back to the 1880s in Washington, D.C. when the Scottish-born scientist Alexander Graham Bell invented the photophone, which transmitted speech on modulated sunlight over several hundred meters. This pre-dates the transmission of speech by radio. More recent work began in 2003 at Nakagawa Laboratory, in Keio University, Japan, using LEDs to transmit data by visible light. Since then there have been numerous research activities focussed on VLC. In 2006, researchers from CICTR at Penn State proposed a combination of power line communication (PLC) and

title: Color of chemicals

text: see is the complementary color, made up of the other visible wavelengths remaining. For example, beta-carotene has maximum absorption at 454 nm (blue light), consequently what visible light remains appears orange . Below is a rough table of wavelengths, colors and complementary colors. This utilizes the scientific CMY and RGB color wheels rather than the traditional RYB color wheel. This can only be used as a very rough guide, for instance if a narrow range of wavelengths within the band 647-700 is absorbed, then the blue and green receptors will be fully stimulated, making cyan, and the red receptor will

title: Visible-light astronomy

text: Earth. There are three main types of telescopes used in visible-light astronomy: Each type of telescope suffers from different types of aberration; refracting telescopes have chromatic aberration, which causes colors to be shown on edges separating light and dark parts of the image, where there should not be such colors. This is due to the lens being unable to focus all colors to the same convergence point. Reflecting telescopes suffer from several types of optical inaccuracies, such as off-axis aberrations near the edges of the field of view. Catadioptric telescopes vary in the types of optical inaccuracies present, as there

title: Light

text: the same intensity (W/m) of visible light do not necessarily appear equally bright. The photometry units are designed to take this into account, and therefore are a better representation of how "bright" a light appears to be than raw intensity. They relate to raw power by a quantity called luminous efficacy, and are used for purposes like determining how to best achieve sufficient illumination for various tasks in indoor and outdoor settings. The illumination measured by a photocell sensor does not necessarily correspond to what is perceived by the human eye, and without filters which may be costly, photocells and

title: Incandescent light bulb

text: 1914, 88.5 million lamps were used, (only 15% with carbon filaments), and by 1945, annual sales of lamps were 795 million (more than 5 lamps per person per year). Of the power consumed by typical incandescent light bulbs, 95% or more is converted into heat rather than visible light. Other electrical light sources are more effective. Luminous "efficacy" of a light source may be defined in two ways. The radiant luminous efficacy (LER) is the ratio of the visible light flux emitted (the "luminous flux") to the total power radiated over all wavelengths. The source luminous efficacy (LES) is the

title: Vision in fishes

text: that with increasing depth the amount of light available decreases quickly. The optical properties of water also lead to different wavelengths of light being absorbed to different degrees. For example, visible light of long wavelengths (e.g. red, orange) is absorbed in less water than light of shorter wavelengths (green, blue). Ultraviolet light (even shorter wavelength than violet) can penetrate deeper than visual spectra Besides these universal qualities of water, different bodies of water may absorb light of different wavelengths due to varying salt and/or chemical presence in the water. Fish eyes are broadly similar to those of other vertebrates –

title: Dental curing light

text: Dental curing light A dental curing light is a piece of dental equipment that is used for polymerization of light cure resin based composites. It can be used on several different dental materials that are curable by light. The light used falls under the visible blue light spectrum. This light is delivered over a range of wavelengths and varies for each type of device. There are four basic types of dental curing light sources: tungsten halogen, light-emitting diodes (LED), plasma arcs, and lasers. The two most common are halogen and LEDs. In the early 1960s, the first light curing resin

title: Phase-out of incandescent light bulbs

text: source is similar in character to that from a Planckian "black body" in spectral distribution, that is, the bulb, as the filament heats up, produces light from wavelengths throughout the visible spectrum. Alternative light sources use phosphors or combinations of mono-chromatic LEDs (red, blue, green) to produce "white" light, giving significantly irregular spectral distributions which can result in color casts in photography and differences of color matching when compared to incandescent light or daylight. Halogen lamps are a type of incandescent lamp with improved efficiency over regular incandescent lamps. Though not as energy efficient as other alternatives, they are up

title: Light-emitting diode

text: practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness. Early LEDs were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays and were commonly seen in digital clocks. Recent

title: Infrared photography

text: with the psychedelic aesthetic that emerged in the late 1960s. Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. "Near infrared" light is closest in wavelength to visible light and "far infrared" is closer to the microwave region of the electromagnetic spectrum. The longer, far infrared wavelengths are about the size of a pin head and the shorter, near infrared ones are the size of cells, or are microscopic. Most manual focus 35 mm SLR and

title: Visible-light astronomy

text: atmosphere. This allows for much clearer observations, as the Earth's atmosphere is not disrupting the image and viewing quality of the telescope, meaning objects can be observed in much greater detail, and much more distant or low-light objects may be observed. Additionally, this means that observations are able to be made at any time, rather than only during the night. The Hubble Space Telescope is a space telescope created by NASA, and was launched into low Earth orbit in 1990. It is still in operation today. The Hubble Space Telescope's four main instruments observe in the near ultraviolet, visible, and

title: Hiding in the Light

text: "showcasing the same image of New York City, viewed through the filters of various wavelengths of light: visible, infrared, ultraviolet, X-ray, gamma ray, microwave, and even a radio image". The episode maintained the previous week's 18-49 rating/share of 1.5/4, with 3.98 million American viewers watching on Fox. This episode explores the wave theory of light as studied by mankind, noting that light has played an important role in scientific progress, with such early experiments from over 2000 years ago involving the camera obscura by the Chinese philosopher Mozi. Tyson describes the work of the 11th century Arabic scientist Ibn al-Haytham,

title: Ultraviolet–visible spectroscopy

text: cm. (This width becomes the path length, formula_14, in the Beer–Lambert law.) Test tubes can also be used as cuvettes in some instruments. The type of sample container used must allow radiation to pass over the spectral region of interest. The most widely applicable cuvettes are made of high quality fused silica or quartz glass because these are transparent throughout the UV, visible and near infrared regions. Glass and plastic cuvettes are also common, although glass and most plastics absorb in the UV, which limits their usefulness to visible wavelengths. Specialized instruments have also been made. These include attaching spectrophotometers

title: Light

text: of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, which is how these animals detect it. Above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the very short (below 360 nm) ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses (such as insects

title: Light field

text: formation method that involves a digital computer. Many of these methods operate at visible wavelengths, and many of those produce light fields. As a result, listing all applications of light fields would require surveying all uses of computational imaging in art, science, engineering, and medicine. In computer graphics, some selected applications are: Image generation and predistortion of synthetic imagery for holographic stereograms is one of the earliest examples of computed light fields, anticipating and later motivating the geometry used in Levoy and Hanrahan's work (Halle 1991, 1994). Modern approaches to light field display explore co-designs of optical elements and compressive

title: Refractive index and extinction coefficient of thin film materials

text: light, λ, since experimentally variables involving thin films are typically measured over a spectrum of wavelengths. The "n" and "k" spectra of a thin film cannot be measured directly, but must be determined indirectly from measurable quantities that depend on them. Spectroscopic reflectance, "R(λ"), is one such measurable quantity. Another, is spectroscopic transmittance, "T(λ)", applicable when the substrate is transparent. Spectroscopic reflectance of a thin film on a substrate represents the ratio of the intensity of light reflected from the sample to the intensity of incident light, measured over a range of wavelengths, whereas spectroscopic transmittance, "T(λ)", represents the ratio

title: Full-spectrum light

text: Full-spectrum light Full-spectrum light is light that covers the electromagnetic spectrum from infrared to near-ultraviolet, or all wavelengths that are useful to plant or animal life; in particular, sunlight is considered full spectrum, even though the solar spectral distribution reaching Earth changes with time of day, latitude, and atmospheric conditions. "Full-spectrum" is not a technical term when applied to an electrical light bulb. Rather, it implies that the product emulates some important quality of natural light. Products marketed as "full-spectrum" may produce light throughout the entire visible spectrum, but without producing an even spectral distribution. Some may not differ substantially

title: Light

text: by more energetic radiation, a process known as fluorescence. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example. This mechanism is used in cathode ray tube television sets and computer monitors. Certain other mechanisms can produce light: When the concept of light is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include: Light is measured with two main alternative sets of units: radiometry consists of measurements of light power at all wavelengths, while photometry measures

title: Full-spectrum light

text: from lights not marketed as "full-spectrum". Color temperature and Color Rendering Index (CRI) are the standards for measuring light. There is no technical definition of "full-spectrum" so it cannot be measured. To compare "full-spectrum" sources requires direct comparison of spectral distribution. The emission spectrum of a light source varies depending on the light generating mechanism. Thermal sources such as incandescent bulbs produce electromagnetic radiation over a broad and continuous range of wavelengths, including infrared and ultraviolet. A black body radiator is the idealized version of a thermal source. As the temperature of a black body radiator increases, the shape of

title: Conservation and restoration of paintings

text: paints to areas of paint loss to restore the "visual unity" of the painting. Conservators need to analyze the inner layers of paintings and their support to identify pigments and unstable layers. They use various tools for types of imaging to disguise materials and damages. Multispectral imaging is the capture of a single image viewed in different wavelengths. For imaging purposes of conservation, paintings are recorded in the wavelengths: ultraviolet (UV), visible (VIS) and infrared (IR). "VIS- Visible Light"- The photo image visible to the naked eye representing the actual colors of the painting. RAK-Raking Light- Lighting the painting from

title: Non-ionizing radiation

text: electromagnetic radiation of all wavelengths, whether visible or not. High-energy visible light is blue-violet light with a higher damaging potential. Infrared (IR) light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometers, which equates to a frequency range between approximately 1 and 430 THz. IR wavelengths are longer than that of visible light, but shorter than that of terahertz radiation microwaves. Bright sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation. Microwaves are

title: Photometer

text: gain parameters of the detector itself. The light sensing element in photon counting devices in NIR, visible and ultraviolet wavelengths is a photomultiplier to achieve sufficient sensitivity. In airborne and space-based remote sensing such photon counters are used at the upper reaches of the electromagnetic spectrum such as the X-ray to far ultraviolet. This is usually due to the lower radiant intensity of the objects being measured as well as the difficulty of measuring light at higher energies using its particle-like nature as compared to the wavelike nature of light at lower frequencies. Conversely, radiometers are typically used for remote

title: Light pollution

text: information, many lighting professionals continue to disparage low-pressure sodium, contributing to its decreased acceptance and specification in lighting standards and therefore its use. Another disadvantage of low-pressure sodium lamps is that some people find the characteristic yellow light very displeasing aesthetically. Because of the increased sensitivity of the human eye to blue and green wavelengths when viewing low-luminances (the Purkinje effect) in the night sky, different sources produce dramatically different amounts of visible skyglow from the same amount of light sent into the atmosphere. In some cases, evaluation of existing plans has determined that more efficient lighting plans are possible.

title: Radar

text: sophisticated methods of signal processing are also used in order to recover useful radar signals. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapour, raindrops, or atmospheric gases (especially oxygen) are avoided in designing

title: Capella

text: are K0III and G1III, although older values are still widely quoted such as G5IIIe + G0III from the Bright Star Catalogue or G8III + G0III by Eggen. Where the context is clear, these two components have been referred to as A and B. The individual apparent magnitudes of the two component stars cannot be directly measured, but their relative brightness has been measured at various wavelengths. They have very nearly equal brightness in the visible light spectrum, with the hotter secondary component generally being found to be a few tenths of a magnitude brighter. A 2016 measurement gives the magnitude

title: International Year of Light

text: Robert Woodrow Wilson (1936) announced the discovery of Cosmic Microwave Background (CMB) Radiation. This radiation is a relic of the light that filled the early cosmos almost 14 billion years ago, that can still be observed today across the sky at much longer wavelengths than visible light, in the domain of microwaves. Finding the CMB represented a triumph for the "Big Bang" description of the Universe. Penzias and Wilson won the Nobel Prize in Physics in 1978 for their discovery. The detection of the CMB triggered a series of increasingly accurate experiments and detailed theoretical calculations over the past fifty

title: Photoinhibition

text: they can lead to production of singlet oxygen. The molecular mechanism(s) of photoinhibition are constantly under discussion. The newest candidate is the manganese mechanism suggested 2005 by the group of Esa Tyystjärvi. A similar mechanism was suggested by the group of Norio Murata, also in 2005. Photoinhibition occurs in all organisms capable of oxygenic photosynthesis, from vascular plants to cyanobacteria. In both plants and cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, and all wavelengths of ultraviolet light are more efficient than wavelengths of visible light. Photoinhibition is a series of reactions that inhibit different

title: Light-emitting diode

text: quantum dot layer and recombine forming an exciton that excites a QD. This scheme is commonly studied for quantum dot display. The tunability of emission wavelengths and narrow bandwidth is also beneficial as excitation sources for fluorescence imaging. Fluorescence near-field scanning optical microscopy (NSOM) utilizing an integrated QD-LED has been demonstrated. In February 2008, a luminous efficacy of 300 lumens of visible light per watt of radiation (not per electrical watt) and warm-light emission was achieved by using nanocrystals. The main types of LEDs are miniature, high-power devices, and custom designs such as alphanumeric or multicolor. These are mostly single-die

title: Effects of blue light technology

text: nine hours of sleep. Just one night of irregular sleep can drastically cause an imbalance in our bodies. Because blue light is the color of the sky, this may be the reason it is extremely sensitive to our eyes. Blue light has been found to delay sleepiness and can affect our circadian rhythm. Wearing yellow tinted sunglasses at night to avoid the blue wavelengths can ensure that you will become naturally tired and may help induce sleep quicker. A research study measured the effect of iPads at full brightness. It was found that after one hour of use, there was

title: Visible light communication

text: used in places such as hospitals, eldercare homes, warehouses, and large, open offices to locate people and control indoor robotic vehicles. There is wireless network that for data transmission uses visible light, and does not use intensity modulation of optical sources. The idea is to use vibration generator instead of optical sources for data transmission. Color shift keying (CSK), outlined in IEEE 802.15.7, is an intensity modulation based modulation scheme for VLC. CSK is intensity-based, as the modulated signal takes on an instantaneous color equal to the physical sum of three (red/green/blue) LED instantaneous intensities. This modulated signal jumps instantaneously,

title: Light therapy

text: emits up to 10,000 lux of light at a specified distance, much brighter than a customary lamp, or a lower intensity of specific wavelengths of light from the blue (460 nm) to the green (525 nm) areas of the visible spectrum. A 1995 study showed that green light therapy at doses of 350 lux produces melatonin suppression and phase shifts equivalent to 10,000 lux white light therapy, but another study published in May 2010 suggests that the blue light often used for SAD treatment should perhaps be replaced by green or white illumination, because of a possible involvement of the

title: Visible light communication

text: in a hypermarket in Lille, France. In June 2015, two Chinese companies, Kuang-Chi and Ping An Bank, partnered to introduce a payment card that communicates information through a unique visible light. In March 2017, Philips set up the first VLC location-based services to shoppers' smartphones in Germany. The installation was presented at EuroShop in Düsseldorf (March 5 – 9 th). As first supermarket in Germany an Edeka supermarket in Düsseldorf-Bilk is using the system, which offers a 30 centimeter positioning accuracy can be achieved, which meets the special demands in food retail. Indoor positioning systems based on VLC can be

title: Optical filter

text: only allow a narrow range of wavelengths (essentially a single colour) to pass. The term "infrared filter" can be ambiguous, as it may be applied to filters to pass infrared (blocking other wavelengths) or to block infrared (only). Infrared-passing filters are used to block visible light but pass infrared; they are used, for example, in infrared photography. Infrared cut-off filters are designed to block or reflect infrared wavelengths but pass visible light. Mid-infrared filters are often used as heat-absorbing filters in devices with bright incandescent light bulbs (such as slide and overhead projectors) to prevent unwanted heating due to infrared

title: Dental curing light

text: the quartz-halogen bulb; this device had longer wavelengths of the visible light spectrum and allowed for greater penetration of the curing light and light energy for resin composites. The halogen curing light replaced the UV curing light. The 1990s presented great improvements in light curing devices. As dental restorative materials advanced, so too did the technology used to cure these materials; the focus was to improve the intensity in order to be able to cure faster and deeper. In 1998 the plasma arc curing light was introduced. It uses a high intensity light source, a fluorescent bulb containing plasma, in

title: Dental curing light

text: composites were developed. This led to the development of the first curing light, called Nuva Light, which was developed by Dentsply/Caulk in the 1970s. Nuva Light used ultraviolet light to cure resin composites. It was discontinued due to this requirement, as well as the fact that the shorter wavelengths of UV light did not penetrate deeply enough into the resin to adequately cure it. During the early 1980s, advances in the area of visible light curing took place, which ultimately led to the creation of a curing device that uses blue light. The next type of curing light developed was

title: Incandescent light bulb

text: sources are radiant efficiencies and efficacies. A similar chart in the article on luminous efficacy compares a broader array of light sources to one another. The spectrum emitted by a blackbody radiator at temperatures of incandescent bulbs does not match the sensitivity characteristics of the human eye. Most of the radiation is not in the range of wavelengths to which the eye is sensitive. Tungsten filaments radiate mostly infrared radiation at temperatures where they remain solid – below . Donald L. Klipstein explains it this way: "An ideal thermal radiator produces visible light most efficiently at temperatures around . Even

title: Spectrophotometry

text: emits IR light as thermal radiation, especially at wavelengths beyond about 5 μm. Another complication is that quite a few materials such as glass and plastic absorb infrared light, making it incompatible as an optical medium. Ideal optical materials are salts, which do not absorb strongly. Samples for IR spectrophotometry may be smeared between two discs of potassium bromide or ground with potassium bromide and pressed into a pellet. Where aqueous solutions are to be measured, insoluble silver chloride is used to construct the cell. Spectroradiometers, which operate almost like the visible region spectrophotometers, are designed to measure the spectral

title: Mirror

text: part of their optical designs, usually to correct optical aberrations. The reflectivity of the mirror coating can be measured using a reflectometer and for a particular metal it will be different for different wavelengths of light. This is exploited in some optical work to make cold mirrors and hot mirrors. A cold mirror is made by using a transparent substrate and choosing a coating material that is more reflective to visible light and more transmissive to infrared light. A hot mirror is the opposite, the coating preferentially reflects infrared. Mirror surfaces are sometimes given thin film overcoatings both to retard

title: Ultraviolet photography

text: Silicon (from which DSLR sensors are made) can respond to wavelengths between 1100-190 nm. Photography based on visible fluorescence induced by UV radiation uses the same ultraviolet illumination as in reflected UV photography. However, the glass barrier filter used on the lens must now absorb or block all ultraviolet and infrared light and must permit only the "visible" radiation to pass. Visible fluorescence is produced in a suitable subject when the shorter, higher energy ultraviolet wavelengths are absorbed, lose some energy and are emitted as longer, lower energy visible wavelengths. UV induced visible fluorescence photography must take place in a

title: Ultraviolet–visible spectroscopy

text: the rate of change in absorbance with wavelength is smallest. Measurements are usually made at a peak to minimize errors produced by errors in wavelength in the instrument, that is errors due to having a different extinction coefficient than assumed. Another important factor is the "purity" of the light used. The most important factor affecting this is the "stray light" level of the monochromator. The detector used is broadband; it responds to all the light that reaches it. If a significant amount of the light passed through the sample contains wavelengths that have much lower extinction coefficients than the nominal

title: Absorbance

text: of magnitude (detections have been demonstrated all the way down to 5 × 10). The theoretical best accuracy for most commercially available non-laser-based instruments is attained in the range near 1 AU. The path length or concentration should then, when possible, be adjusted to achieve readings near this range. Typically, absorbance of a dissolved substance is measured using absorption spectroscopy. This involves shining a light through a solution and recording how much light and what wavelengths were transmitted onto a detector. Using this information, the wavelengths that were absorbed can be determined. First, measurements on a "blank" are taken using

title: History of the telescope

text: a very narrow field (tens of arcsec), and current systems operating on several 8-10m telescopes work mainly in near-infrared wavelengths for single-object observations. Developments of adaptive optics include systems with multiple lasers over a wider corrected field, and/or working above kiloHertz rates for good correction at visible wavelengths; these are currently in progress but not yet in routine operation as of 2015. The twentieth century saw the construction of telescopes which could produce images using wavelengths other than visible light starting in 1931 when Karl Jansky discovered astronomical objects gave off radio emissions; this prompted a new era of observational

title: Filter fluorometer

text: Filter fluorometer A filter fluorometer is a type of fluorometer that may be employed in fluorescence spectroscopy. In the fluorometer, a light source emits light of an excitation wavelength that is relevant to the compound to be measured. Filter fluorometers produce specific excitation and emission wavelengths by using optical filters. The filter blocks other wavelengths but transmits wavelengths relevant to the compound. The light passes through the sample to be measured, and a certain wavelength is absorbed while a longer wavelength is emitted. The emitted light is measured by a detector. By changing the optical filter, different substances can be

title: Faster-than-light

text: by the tube. In physics, the speed of light in a vacuum is assumed to be a constant. However, hypotheses exist that the speed of light is variable. The speed of light is a dimensional quantity and so cannot be measured. Measurable quantities in physics are, without exception, dimensionless, although they are often constructed as ratios of dimensional quantities. For example, when the height of a mountain is measured, what is really measured is the ratio of its height to the length of a meter stick. The conventional SI system of units is based on seven basic dimensional quantities, namely

title: Color

text: Subtractive coloring uses dyes, inks, pigments, or filters to absorb some wavelengths of light and not others. The color that a surface displays comes from the parts of the visible spectrum that are not absorbed and therefore remain visible. Without pigments or dye, fabric fibers, paint base and paper are usually made of particles that scatter white light (all colors) well in all directions. When a pigment or ink is added, wavelengths are absorbed or "subtracted" from white light, so light of another color reaches the eye. If the light is not a pure white source (the case of nearly

title: History of the metre

text: the light from a discharge lamp), both of which are advantageous for interferometry. The shortcomings of the krypton standard were demonstrated by the measurement of the wavelength of the light from a methane-stabilized helium–neon laser ("λ" ≈ 3.39 µm). The krypton line was found to be asymmetrical, so different wavelengths could be found for the laser light depending on which point on the krypton line was taken for reference. The asymmetry also affected the precision to which the wavelengths could be measured. Developments in electronics also made it possible for the first time to measure the frequency of light in

title: Visible spectrum

text: 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

title: Absorption (electromagnetic radiation)

text: absorbance of an object quantifies how much of the incident light is absorbed by it (instead of being reflected or refracted). This may be related to other properties of the object through the Beer–Lambert law. Precise measurements of the absorbance at many wavelengths allow the identification of a substance via absorption spectroscopy, where a sample is illuminated from one side, and the intensity of the light that exits from the sample in every direction is measured. A few examples of absorption are ultraviolet–visible spectroscopy, infrared spectroscopy, and X-ray absorption spectroscopy. Understanding and measuring the absorption of electromagnetic radiation has a

title: Absorption (electromagnetic radiation)

text: allows for material identification. In optics, sunglasses, colored filters, dyes, and other such materials are designed specifically with respect to which visible wavelengths they absorb, and in what proportions. In biology, photosynthetic organisms require that light of the appropriate wavelengths be absorbed within the active area of chloroplasts, so that the light energy can be converted into chemical energy within sugars and other molecules. In physics, the D-region of Earth's ionosphere is known to significantly absorb radio signals that fall within the high-frequency electromagnetic spectrum. In nuclear physics, absorption of nuclear radiations can be used for measuring the fluid levels,

title: Mass attenuation coefficient

text: solution, the concentrations of each can be calculated using a light absorption analysis. First, the mass attenuation coefficients of each individual solute or solvent, ideally across a broad spectrum of wavelengths, must be measured or looked up. Second, the attenuation coefficient of the actual solution must be measured. Finally, using the formula the spectrum can be fitted using "ρ", "ρ", … as adjustable parameters, since "μ" and each are functions of wavelength. If there are "N" solutes or solvents, this procedure requires "at least" "N" measured wavelengths to create a solvable system of simultaneous equations, although using more wavelengths gives

title: Photoinhibition

text: follows simple first-order kinetics if measured from a lincomycin-treated leaf, cyanobacterial or algal cells, or isolated thylakoid membranes in which concurrent repair does not disturb the kinetics. Data from the group of W. S. Chow indicate that in leaves of pepper ("Capsicum annuum"), the first-order pattern is replaced by a pseudo-equilibrium even if the repair reaction is blocked. The deviation has been explained by assuming that photoinhibited PSII centers protect the remaining active ones. Both visible and ultraviolet light cause photoinhibition, ultraviolet wavelengths being much more damaging. Some researchers consider ultraviolet and visible light induced photoinhibition as a two different

title: Attenuation

text: radiation reaches the sea-surface, the shortwave radiation is attenuated by the water, and the intensity of light decreases exponentially with water depth. The intensity of light at depth can be calculated using the Beer-Lambert Law. In clear open waters, visible light is absorbed at the longest wavelengths first. Thus, red, orange, and yellow wavelengths are absorbed at higher water depths, and blue and violet wavelengths reach the deepest in the water column. Because the blue and violet wavelengths are absorbed last compared to the other wavelengths, open ocean waters appear deep-blue to the eye. In near-shore (coastal) waters, sea water

title: Incandescent light bulb

text: depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a continuous spectrum. The useful part of the emitted energy is visible light, but most energy is given off as heat in the near-infrared wavelengths. Three-way light bulbs have two filaments and three conducting contacts in their bases. The filaments share a common ground, and can be lit separately or together. Common wattages include 30–70–100, 50–100–150, and 100–200–300, with the first two numbers referring to the individual filaments, and the third giving the combined wattage. Most light bulbs have either clear

title: Mie scattering

text: travel through the high-density air near the Earth's surface. In contrast, the water droplets that make up clouds are of a comparable size to the wavelengths in visible light, and the scattering is described by Mie's model rather than that of Rayleigh. Here, all wavelengths of visible light are scattered approximately identically, and the clouds therefore appear to be white or grey. The Rayleigh–Gans approximation is an approximate solution to light scattering when the relative refractive index of the particle is close to unity, and its size is much smaller in comparison to the wavelength of light divided by |"n"

title: Normalized difference vegetation index

text: well as other visible wavelengths) and quite dark in the near-infrared. The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm). The more leaves a plant has, the more these wavelengths of light are affected, respectively. Since early instruments of Earth Observation, such as NASA's ERTS and NOAA's AVHRR, acquired data in visible and near-infrared, it was natural to exploit the strong differences in plant reflectance to determine their spatial distribution in

title: Xenon monochloride

text: was attributed to . The first laser was developed in 1980. This type of laser is likely to be tunable over a wide range of wavelengths (30 nm) in the visible spectrum. This is true even if the absorption phenomena occur on the side of shorter wavelengths and therefore limits the laser action at the red region of the electromagnetic spectrum from light emission. Solid state experiments with suggest that the gaseous state is more suitable for the development of this type of laser. The measured amplification was correct in the solid state. The liquid state seems like an ideal

title: Spectral color

text: some of the colors that are spectral colors are: 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. 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.

title: Environmental monitoring

text: radiation that is emitted or reflected by the object or surrounding area being observed. Reflected sunlight is the most common source of radiation measured by passive sensors and in environmental remote sensing, the sensors used are tuned to specific wavelengths from far infrared through visible light frequencies to the far ultraviolet. The volumes of data that can be collected are very large and require dedicated computational support . The output of data analysis from remote sensing are false colour images which differentiate small differences in the radiation characteristics of the environment being monitored. With a skilful operator choosing specific channels

title: Visible spectrum

text: 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)

title: Dichroism

text: Dichroism In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with dispersion), "or" one in which light rays having different polarizations are absorbed by different amounts. The original meaning of "dichroic", from the Greek "dikhroos", two-coloured, refers to any optical device which can split a beam of light into two beams with differing wavelengths. Such devices include mirrors and filters, usually treated with optical coatings, which are designed to reflect light over a certain range of wavelengths, and transmit light which is

title: Optical spectrometer

text: be used for both visible and UV light. The exact choice of detector depends on the wavelengths of light to be recorded. A spectrograph is sometimes called polychromator, as an analogy to monochromator. Optical spectrometer An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization state. The independent variable is usually the wavelength of the light or a unit directly proportional

title: Subtractive color

text: Subtractive color A subtractive color model explains the mixing of a limited set of dyes, inks, paint pigments or natural colorants to create a wider range of colors, each the result of partially or completely subtracting (that is, absorbing) some wavelengths of light and not others. The color that a surface displays depends on which parts of the visible spectrum are not absorbed and therefore remain visible. Subtractive color systems start with light, presumably white light. Colored inks, paints, or filters between the watchers and the light source or reflective surface "subtract" wavelengths from the light, giving it color. If

title: Light effects on circadian rhythm

text: of white light. Exposure to monochromatic light at the wavelengths of 460 nm and 550 nm on two control groups yielded results showing decreased sleepiness at 460 nm tested over two groups and a control group. Additionally, in the same study but testing thermoregulation and heart rate researchers found significantly increased heart rate in 460 nm light over the course of a 1.5 hour exposure period. In a study done on the effect of lighting intensity on delta waves, a measure of sleepiness, high levels of lighting (1700 lux) showed lower levels of delta waves measured through an EEG than

title: Cauchy's equation

text: dispersive regions, and more accurately models a material's refractive index across the ultraviolet, visible, and infrared spectrum. Cauchy's equation Cauchy's equation is an empirical relationship between the refractive index and wavelength of light for a particular transparent material. It is named for the mathematician Augustin-Louis Cauchy, who defined it in 1836. The most general form of Cauchy's equation is where "n" is the refractive index, λ is the wavelength, "B", "C", "D", etc., are coefficients that can be determined for a material by fitting the equation to measured refractive indices at known wavelengths. The coefficients are usually quoted for λ

title: Astronomy

text: interstellar gas, pulsars, and active galactic nuclei. Infrared astronomy is founded on the detection and analysis of infrared radiation, wavelengths longer than red light and outside the range of our vision. The infrared spectrum is useful for studying objects that are too cold to radiate visible light, such as planets, circumstellar disks or nebulae whose light is blocked by dust. The longer wavelengths of infrared can penetrate clouds of dust that block visible light, allowing the observation of young stars embedded in molecular clouds and the cores of galaxies. Observations from the Wide-field Infrared Survey Explorer (WISE) have been particularly

title: In the Light of What We Know

text: In the Light of What We Know In the Light of What We Know is the debut novel of Zia Haider Rahman. First published by Farrar, Straus and Giroux, the novel was released in the spring of 2014 to international critical acclaim and earned its author the James Tait Black Memorial Prize, Britain's oldest literary prize. and the inaugural International Ranald McDonald prize 2016. The novel has already been translated into Dutch, French and Portuguese and is to be translated into several other languages. Much of the novel is set during the war in Afghanistan at the beginning of the

title: In the Light of What We Know

text: shortlisted for the Goldsmiths Prize 2014 and nominated for the Folio Prize 2015. The author was shortlisted for New Writer of the Year award at the National Book Awards (UK) 2014. In the Light of What We Know In the Light of What We Know is the debut novel of Zia Haider Rahman. First published by Farrar, Straus and Giroux, the novel was released in the spring of 2014 to international critical acclaim and earned its author the James Tait Black Memorial Prize, Britain's oldest literary prize. and the inaugural International Ranald McDonald prize 2016. The novel has already been