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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 . Living things on dry land would be severely damaged by ultraviolet radiation from the Sun
Sun
if most of it were not filtered out by the Earth's atmosphere. More-energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. Ultraviolet
Ultraviolet
is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has effects both beneficial and harmful to human health
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Ultraviolet (other)
ULTRAVIOLET refers to electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays
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UV (other)
UV usually refers to ultraviolet radiation. UV may also refer to: CONTENTS * 1 Universities * 2 Political parties * 3 Other uses * 4 See also UNIVERSITIES * University of Valencia , Spain * University of Valparaíso
University of Valparaíso
, Chile * University of Victoria , Canada * University of Vienna
University of Vienna
, Austria * University of Vermont , United States * University of Virginia , United States * University of the Visayas , PhilippinesPOLITICAL PARTIES * Valdostan Union , Italy * Young Liberals of Norway OTHER USES * Ganz UV , a Hungarian tram type * UV mapping
UV mapping
, the 3D modeling process of making a 2D image representation of a 3D model * Unique visitor , a unit for measuring the popularity of a website, often used by the advertising industry * Unmanned vehicle * UV , a Korean hip-hop duo starring Yoo Se-yoon and Muzie. * UV Vodka, a brand produced by Phillips Distilling Company SEE ALSO * All pages beginning with "UV" * Ultraviolet (other) This disambiguation page lists articles associated with the title UV. If an internal link led you here, you may wish to change the link to point directly to the intended article
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Electric Arc
An ELECTRIC ARC or ARC DISCHARGE is an electrical breakdown of a gas that produces an ongoing electrical discharge . The current through a normally nonconductive medium such as air produces a plasma ; the plasma may produce visible light . An arc discharge is characterized by a lower voltage than a glow discharge , and it relies on thermionic emission of electrons from the electrodes supporting the arc. An archaic term is VOLTAIC ARC, as used in the phrase "voltaic arc lamp". CONTENTS * 1 History * 2 Overview * 3 Uses * 3.1 Guiding the arc * 4 Undesired arcing * 5 Arc suppression * 6 See also * 7 References * 8 External links HISTORY Natural Lightning is now considered an electric spark , not electric arc. The phenomenon is believed to be first described by Sir Humphry Davy in an 1801 paper published in William Nicholson\'s Journal of Natural Philosophy, Chemistry and the Arts . However, Davy's description was not an electric arc as this phenomenon is considered by the modern science: "This is evidently the description, not of an arc, but of a spark. For the essence of an arc is that it should be continuous, and that the poles should not be in contact after it has once started
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Arc Welder
ARC WELDING is a process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals when cool result in a binding of the metals. It is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes . The welding region is usually protected by some type of shielding gas , vapor, or slag. Arc welding processes may be manual, semi-automatic, or fully automated. First developed in the late part of the 19th century, arc welding became commercially important in shipbuilding during the Second World War. Today it remains an important process for the fabrication of steel structures and vehicles. CONTENTS * 1 Power supplies * 2 Consumable electrode methods * 3 Non-consumable electrode methods * 4 Corrosion
Corrosion
issues * 5 Safety issues * 5.1 Heat, fire, and explosion hazard * 5.2 Eye damage * 5.3 Inhaled matter * 5.4 Interference with pacemakers * 6 History * 7 See also * 8 References * 8.1 Notes * 8.2 Sources * 9 Further reading * 10 External links POWER SUPPLIES Engine driven welder capable of AC/DC welding. A diesel powered welding generator (the electric generator is on the left) as used in Indonesia
Indonesia

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Eye Protection
EYE PROTECTION is protective gear for the eyes , which comes in many types depending upon the threat that is to be reduced. The threats can be particles , light , wind blast , heat , sea spray or some type of ball or puck used in sports. CONTENTS * 1 Goggles
Goggles
* 2 Protection against light * 3 Other protection * 4 Helmets and visors * 5 Pricing * 6 Gallery * 7 See also * 8 References * 9 External links GOGGLES Main article: Goggles
Goggles
Goggles
Goggles
are forms of protective eyewear that usually enclose or protect the eye area in order to prevent particulates, infectious fluids, or chemicals from striking the eyes. For example, when swimming , goggles protect the eyes from salt or chlorine in the pool. PROTECTION AGAINST LIGHTThe human eye is sensitive to intense light because it damages the retina and can even blind the individual. There are many different types of eye protection against light suited for different applications. The most common forms of eye protection against light are sunglasses . These primarily protect against UV light from the sun and help increase visibility in bright conditions. They often tend to be fashionable as well as practical. Laser protection eyewear is similar but will filter out a particular (or small range of) wavelength(s), customized to the laser being viewed
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Photokeratitis
PHOTOKERATITIS or ULTRAVIOLET KERATITIS is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet (UV) rays from either natural (e.g. intense sunlight ) or artificial (e.g. the electric arc during welding ) sources. Photokeratitis
Photokeratitis
is akin to a sunburn of the cornea and conjunctiva , and is not usually noticed until several hours after exposure. Symptoms include increased tears and a feeling of pain, likened to having sand in the eyes. The injury may be prevented by wearing eye protection that blocks most of the ultraviolet radiation, such as welding goggles with the proper filters, a welder's helmet, sunglasses rated for sufficient UV protection, or appropriate snow goggles. The condition is usually managed by removal from the source of ultraviolet radiation, covering the corneas, and administration of pain relief. Photokeratitis
Photokeratitis
is known by a number of different terms including: SNOW BLINDNESS, ARC EYE, WELDER\'S FLASH, BAKE EYES, CORNEAL FLASH BURNS, SAND MAN\'S EYE, FLASH BURNS, NIPHABLEPSIA, POTATO EYE, or KERATOCONJUNCTIVITIS PHOTOELECTRICA. CONTENTS * 1 Signs and symptoms * 2 Diagnosis * 3 Cause * 4 Prevention * 5 Treatment * 6 See also * 7 References * 8 External links SIGNS AND SYMPTOMSCommon symptoms include pain, intense tears , eyelid twitching , discomfort from bright light, and constricted pupils
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Sunburn
SUNBURN is a form of radiation burn that affects living tissue, such as skin , that results from an overexposure to ultraviolet (UV) radiation, commonly from the sun . Common symptoms in humans and other animals include red or reddish skin that is hot to the touch, pain , general fatigue, and mild dizziness. An excess of UV radiation can be life-threatening in extreme cases. Exposure of the skin to lesser amounts of UV radiation will often produce a suntan . Excessive UV radiation is the leading cause of primarily non-malignant skin tumors . Sunscreen is widely agreed to prevent sunburn and some types of skin cancer . Clothing, including hats, is considered the preferred skin protection method. Moderate sun tanning without burning can also prevent subsequent sunburn, as it increases the amount of melanin , a photoprotective pigment that is the skin's natural defense against overexposure. Importantly, both sunburn and the increase in melanin production are triggered by direct DNA damage . When the skin cells' DNA is overly damaged by UV radiation, type I cell-death is triggered and the skin is replaced
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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 . The electromagnetic spectrum includes, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared radiation, visible light , ultraviolet radiation, X-rays and gamma rays . Electromagnetic waves are produced whenever charged particles are accelerated , and these waves can subsequently interact with other charged particles. EM waves carry energy , momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact
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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. Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. Wavelength
Wavelength
depends on the medium (for example, vacuum, air, or water) that a wave travels through. Examples of wave-like phenomena are sound waves , light , water waves and periodic electrical signals in a conductor . A sound wave is a variation in air pressure , while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary. Water waves are variations in the height of a body of water
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PHz
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. CONTENTS * 1 Definition * 2 History * 3 Applications * 3.1 Vibration * 3.2 Electromagnetic radiation
Electromagnetic radiation
* 3.3 Computers * 4 SI multiples * 5 See also * 6 Notes and references * 7 External links DEFINITIONThe hertz is equivalent to cycles per second , i.e., "1/second" or s 1 {displaystyle {text{s}}^{-1}}
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Terahertz (unit)
The HERTZ (symbol: Hz) is the derived unit of frequency in the 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. CONTENTS * 1 Definition * 2 History * 3 Applications * 3.1 Vibration * 3.2 Electromagnetic radiation * 3.3 Computers * 4 SI multiples * 5 See also * 6 Notes and references * 7 External links DEFINITIONThe hertz is equivalent to cycles per second , i.e., "1/second" or s 1 {displaystyle {text{s}}^{-1}}
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Visible 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 is the Sun . 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. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems , electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence . For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey
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X-ray
X-RADIATION (composed of X-RAYS) is a form of electromagnetic radiation . Most X-rays have a wavelength ranging from 0.01 to 10 nanometers , corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV . X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays . In many languages, X-radiation is referred to with terms meaning RöNTGEN RADIATION, after the German scientist Wilhelm Röntgen , who usually is credited as its discoverer, and who had named it _X-radiation_ to signify an unknown type of radiation. Spelling of _X-ray(s)_ in the English language includes the variants _x-ray(s)_, _xray(s)_, and _X ray(s)_
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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". The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a principal source of vitamin D3 and a mutagen . Sunlight
Sunlight
takes about 8.3 minutes to reach Earth
Earth
from the surface of the Sun. A photon starting at the center of the Sun
Sun
and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface
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Mercury-vapor Lamp
A MERCURY-VAPOR LAMP is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light . The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor ; in either case, the outer bulb provides thermal insulation , protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube. Mercury vapor lamps are more energy efficient than incandescent and most fluorescent lights , with luminous efficacies of 35 to 65 lumens/watt. Their other advantages are a long bulb lifetime in the range of 24,000 hours and a high intensity, clear white light output. For these reasons, they are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights . Clear mercury lamps produce white light with a bluish-green tint due to mercury's combination of spectral lines. This is not flattering to human skin color , so such lamps are typically not used in retail stores. "Color corrected" mercury bulbs overcome this problem with a phosphor on the inside of the outer bulb that emits white light. They offer better color rendition than the more efficient high or low-pressure sodium vapor lamps . They operate at an internal pressure of around one atmosphere and require special fixtures, as well as an electrical ballast
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