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Light
LIGHT is electromagnetic radiation within a certain portion of the electromagnetic spectrum . The word usually refers to VISIBLE LIGHT, which 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 × 10−7 to 7.00 × 10−7 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
Earth
is the Sun
Sun
. Sunlight
Sunlight
provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the energy used by living things
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Electromagnetic Radiation
In physics , ELECTROMAGNETIC RADIATION (EM RADIATION or EMR) refers to the waves (or their quanta, photons ) of the electromagnetic field , propagating (radiating) through space carrying electromagnetic radiant energy . It includes radio waves , microwaves , infrared , (visible) light , ultraviolet , X- , and gamma radiation. Classically , electromagnetic radiation consists of ELECTROMAGNETIC WAVES, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum . The oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave . The wavefront of electromagnetic waves emitted from a point source (such as a lightbulb) is a sphere . The position of an electromagnetic wave within the electromagnetic spectrum could be characterized by either its frequency of oscillation or its wavelength
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Visible Light (other)
VISIBLE LIGHT may refer to light , or to: * The visible spectrum * A work included in The Collected Short Fiction of C. J. Cherryh
The Collected Short Fiction of C. J. Cherryh
This disambiguation page lists articles associated with the title VISIBLE LIGHT. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from "https://en.wikipedia.org/w/index.php?title=Visible_light_(other) additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy .® is a registered trademark of the Wikimedia Foundation, Inc
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Electromagnetic Spectrum
The ELECTROMAGNETIC SPECTRUM is a collective term; referring to the entire range and scope of frequencies of electromagnetic radiation and their respective, associated photon wavelengths. The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom . Visible light lies toward the shorter end, with wavelengths from 400 to 700 nanometres . The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length . Until the middle of the 20th century it was believed by most physicists that this spectrum was infinite and continuous . Nearly all types of electromagnetic radiation can be used for spectroscopy , to study and characterize matter
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Visual Perception
VISUAL PERCEPTION is the ability to interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. The resulting perception is also known as visual perception, EYESIGHT, SIGHT, or VISION (adjectival form : visual, optical, or ocular). The various physiological components involved in vision are referred to collectively as the visual system , and are the focus of much research in linguistics , psychology , cognitive science , neuroscience , and molecular biology , collectively referred to as vision science
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Human Eye
The HUMAN EYE is an organ which reacts to light and pressure. As a sense organ , the mammalian eye allows vision . Human eyes help provide a three dimensional, moving image, normally coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can differentiate between about 10 million colors and is possibly capable of detecting a single photon . Similar to the eyes of other mammals , the human eye's non-image-forming photosensitive ganglion cells in the retina receive light signals which affect adjustment of the size of the pupil, regulation and suppression of the hormone melatonin and entrainment of the body clock
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Wavelength
In physics , the WAVELENGTH of a sinusoidal wave is the SPATIAL PERIOD of the wave—the distance over which the wave's shape repeats, and thus the inverse of the spatial frequency . It is usually determined by considering the distance between consecutive corresponding points of the same phase , such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves , as well as other spatial wave patterns. Wavelength is commonly designated by the Greek letter _lambda _ (λ). The concept can also be applied to periodic waves of non-sinusoidal shape. The term _wavelength_ is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids
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Nanometre
The NANOMETRE (International spelling as used by the International Bureau of Weights and Measures ; SI symbol: NM) or NANOMETER (American spelling ) is a unit of length in the metric system , equal to one billionth of a metre (6991100000000000000♠0.000000001 m). The name combines the SI prefix
SI prefix
nano- (from the Ancient Greek
Ancient Greek
νάνος, nanos, "dwarf") with the parent unit name metre (from Greek μέτρον, metrοn, "unit of measurement"). It can be written in scientific notation as 6991100000000000000♠1×10−9 m, in engineering notation as 1 E−9 m, and is simply 1/7009100000000000000♠1000000000 metres. One nanometre equals ten ångströms . When used as a prefix for something other than a unit of measure (as in "nanoscience"), NANO refers to nanotechnology , or phenomena typically occurring on a scale of nanometres (see nanoscopic scale )
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Infrared
INFRARED RADIATION, or simply INFRARED or IR, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light , and is therefore invisible, although it is sometimes loosely called INFRARED LIGHT. It extends from the nominal red edge of the visible spectrum at 700 nanometers (frequency 430 THz ), to 1000000 nm (300 GHz ) (although people can see infrared up to at least 1050 nm in experiments ). Most of the thermal radiation emitted by objects near room temperature is infrared. Like all EMR, IR carries radiant energy , and behaves both like a wave and like its quantum particle, the photon . Infrared
Infrared
was discovered in 1800 by astronomer Sir William Herschel
William Herschel
, who discovered a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a thermometer
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Ultraviolet
ULTRAVIOLET (UV) is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays . UV radiation constitutes about 10% of the total light output of the Sun, and is thus present in sunlight . It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps , tanning lamps , and black lights . Although it is not considered an ionizing radiation because its photons lack the energy to ionize atoms , long-wavelength ultraviolet radiation can cause chemical reactions and causes many substances to glow or fluoresce . Consequently, the biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules. Suntan , freckling and sunburn are familiar effects of over-exposure, along with higher risk of skin cancer
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Frequency
FREQUENCY is the number of occurrences of a repeating event per unit time . It is also referred to as TEMPORAL FREQUENCY, which emphasizes the contrast to spatial frequency and angular frequency . The PERIOD is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second (that is, 60 seconds divided by 120 beats ). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio (sound ) signals, radio waves , and light
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Terahertz (unit)
The HERTZ (symbol: Hz) is the derived unit of frequency in the International System of Units
International System of Units
(SI) and is defined as one cycle per second . It is named for Heinrich Rudolf Hertz
Hertz
, the first person to provide conclusive proof of the existence of electromagnetic waves . Hertz
Hertz
are commonly expressed in multiples : kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), and terahertz (1012 Hz, THz). Some of the unit's most common uses are in the description of sine waves and musical tones , particularly those used in radio - and audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven
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Sun
The SUN is the star at the center of the Solar System
Solar System
. It is a nearly perfect sphere of hot plasma , with internal convective motion that generates a magnetic field via a dynamo process . It is by far the most important source of energy for life on Earth
Earth
. Its diameter is about 109 times that of Earth, and its mass is about 330,000 times that of Earth, accounting for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen , carbon , neon , and iron . The Sun
Sun
is a G-type main-sequence star (G2V) based on its spectral class . As such, it is informally referred to as a yellow dwarf. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud
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Sunlight
SUNLIGHT is a portion of the electromagnetic radiation given off by the Sun
Sun
, in particular infrared , visible , and ultraviolet light. On Earth
Earth
, sunlight is filtered through Earth\'s atmosphere , and is obvious as daylight when the Sun
Sun
is above the horizon . When the direct solar radiation is not blocked by clouds , it is experienced as SUNSHINE, a combination of bright light and radiant heat . When it is blocked by clouds or reflects off other objects , it is experienced as diffused light. The World Meteorological Organizationuses the term "sunshine duration " to mean the cumulative time during which an area receives direct irradiance from the Sun
Sun
of at least 120 watts per square meter . Other sources indicate an "Average over the entire earth" of "164 Watts per square meter over a 24 hour day"
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Plants
PLANTS are mainly multicellular , predominantly photosynthetic eukaryotes of the kingdom PLANTAE. The term is today generally limited to the GREEN PLANTS, which form an unranked clade VIRIDIPLANTAE (Latin for "green plants"). This includes the flowering plants , conifers and other gymnosperms , ferns , clubmosses , hornworts , liverworts , mosses and the green algae , and excludes the red and brown algae . Historically, plants formed one of two kingdoms covering all living things that were not animals , and both algae and fungi were treated as plants; however all current definitions of "plant" exclude the fungi and some algae, as well as the prokaryotes (the archaea and bacteria ). Green plants have cell walls containing cellulose and obtain most of their energy from sunlight via photosynthesis by primary chloroplasts , derived from endosymbiosis with cyanobacteria . Their chloroplasts contain chlorophylls a and b, which gives them their green color
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