[{"@context":"http:\/\/schema.org\/","@type":"BlogPosting","@id":"https:\/\/wiki.edu.vn\/en\/wiki5\/lux-wikipedia\/#BlogPosting","mainEntityOfPage":"https:\/\/wiki.edu.vn\/en\/wiki5\/lux-wikipedia\/","headline":"Lux – Wikipedia","name":"Lux – Wikipedia","description":"before-content-x4 SI derived unit of illuminance after-content-x4 The lux (symbol: lx) is the unit of illuminance, or luminous flux per","datePublished":"2014-08-07","dateModified":"2014-08-07","author":{"@type":"Person","@id":"https:\/\/wiki.edu.vn\/en\/wiki5\/author\/lordneo\/#Person","name":"lordneo","url":"https:\/\/wiki.edu.vn\/en\/wiki5\/author\/lordneo\/","image":{"@type":"ImageObject","@id":"https:\/\/secure.gravatar.com\/avatar\/c9645c498c9701c88b89b8537773dd7c?s=96&d=mm&r=g","url":"https:\/\/secure.gravatar.com\/avatar\/c9645c498c9701c88b89b8537773dd7c?s=96&d=mm&r=g","height":96,"width":96}},"publisher":{"@type":"Organization","name":"Enzyklop\u00e4die","logo":{"@type":"ImageObject","@id":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","url":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","width":600,"height":60}},"image":{"@type":"ImageObject","@id":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","url":"https:\/\/wiki.edu.vn\/wiki4\/wp-content\/uploads\/2023\/08\/download.jpg","width":100,"height":100},"url":"https:\/\/wiki.edu.vn\/en\/wiki5\/lux-wikipedia\/","wordCount":6303,"articleBody":"     (adsbygoogle = window.adsbygoogle || []).push({});before-content-x4SI derived unit of illuminance       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI).[1][2] It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a model of human visual brightness perception, standardized by the CIE and ISO.[3] In English, “lux” is used as both the singular and plural form.[4]The word is derived from the Latin word for “light”, lux.       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4Table of ContentsExplanation[edit]Illuminance[edit]Relationship between illuminance and irradiance[edit]Use in video-camera specifications[edit]Non-SI units of illuminance[edit]Legacy Unicode symbol[edit]SI photometry units[edit]See also[edit]References[edit]External links[edit]Explanation[edit]Illuminance[edit]Illuminance is a measure of how much luminous flux is spread over a given area.  One can think of luminous flux (with the unit lumen) as a measure of the total “amount” of visible light present, and the illuminance as a measure of the intensity of illumination on a surface. A given amount of light will illuminate a surface more dimly if it is spread over a larger area, so illuminance is inversely proportional to area when the luminous flux is held constant.One lux is equal to one lumen per square metre:1\u00a0lx\u00a0= 1\u00a0lm\/m2 = 1\u00a0cd\u00b7sr\/m2.A flux of 1000\u00a0lumens, spread uniformly over an area of 1 square metre, lights up that square metre with an illuminance of 1000\u00a0lux. However, the same 1000\u00a0lumens spread out over 10 square metres produces a dimmer illuminance of only 100\u00a0lux.       (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4Achieving an illuminance of 500\u00a0lx might be possible in a home kitchen with a single fluorescent light fixture with an output of 12000\u00a0lumens. To light a factory floor with dozens of times the area of the kitchen would require dozens of such fixtures. Thus, lighting a larger area to the same illuminance (lux) requires a greater luminous flux (lumen).As with other named SI units, SI prefixes can be used. For example, 1\u00a0kilolux (klx) is 1000\u00a0lx.Here are some examples of the illuminance provided under various conditions:Illuminance (lux)Surfaces illuminated by0.0001Moonless, overcast night sky (starlight)[5]0.002Moonless clear night sky with airglow[5]0.05\u20130.3Full moon on a clear night[6]3.4Dark limit of civil twilight under a clear sky[7]20\u201350Public areas with dark surroundings[8]50Family living room lights (Australia, 1998)[9]80Office building hallway\/toilet lighting[10][11]100Very dark overcast day[5]150Train station platforms[12]320\u2013500Office lighting[9][13][14][15]400Sunrise or sunset on a clear day.1000Overcast day;[5] typical TV studio lighting10,000\u201325,000Full daylight (not direct sun)[5]32,000\u2013100,000Direct sunlightThe illuminance provided by a light source on a surface perpendicular to the direction to the source is a measure of the strength of that source as perceived from that location. For instance, a star of apparent magnitude 0 provides 2.08 microlux (\u03bclx) at the Earth’s surface.[16] A barely perceptible magnitude 6 star provides 8 nanolux (nlx).[17] The unobscured Sun provides an illumination of up to 100\u00a0kilolux (klx) on the Earth’s surface, the exact value depending on time of year and atmospheric conditions. This direct normal illuminance is related to the solar illuminance constant Esc, equal to 128000\u00a0lux (see Sunlight and Solar constant).The illuminance on a surface depends on how the surface is tilted with respect to the source. For example, a pocket flashlight aimed at a wall will produce a given level of illumination if aimed perpendicular to the wall, but if the flashlight is aimed at increasing angles to the perpendicular (maintaining the same distance), the illuminated spot becomes larger and so is less highly illuminated. When a surface is tilted at an angle to a source, the illumination provided on the surface is reduced because the tilted surface subtends a smaller solid angle from the source, and therefore it receives less light. For a point source, the illumination on the tilted surface is reduced by a factor equal to the cosine of the angle between a ray coming from the source and the normal to the surface.[18] In practical lighting problems, given information on the way light is emitted from each source and the distance and geometry of the lighted area, a numerical calculation can be made of the illumination on a surface by adding the contributions of every point on every light source.Relationship between illuminance and irradiance[edit]Like all photometric units, the lux has a corresponding “radiometric” unit. The difference between any photometric unit and its corresponding radiometric unit is that radiometric units are based on physical power, with all wavelengths being weighted equally, while photometric units take into account the fact that the human eye’s image-forming visual system is more sensitive to some wavelengths than others, and accordingly every wavelength is given a different weight. The weighting factor is known as the luminosity function.The lux is one lumen per square metre (lm\/m2), and the corresponding radiometric unit, which measures irradiance, is the watt per square metre (W\/m2). There is no single conversion factor between lux and W\/m2; there is a different conversion factor for every wavelength, and it is not possible to make a conversion unless one knows the spectral composition of the light.The peak of the luminosity function is at 555\u00a0nm (green); the eye’s image-forming visual system is more sensitive to light of this wavelength than any other. For monochromatic light of this wavelength, the amount of illuminance for a given amount of irradiance is maximum: 683.002\u00a0lx per 1\u00a0W\/m2; the irradiance needed to make 1\u00a0lx at this wavelength is about 1.464\u00a0mW\/m2. Other wavelengths of visible light produce fewer lux per watt-per-meter-squared. The luminosity function falls to zero for wavelengths outside the visible spectrum.For a light source with mixed wavelengths, the number of lumens per watt can be calculated by means of the luminosity function. In order to appear reasonably “white”, a light source cannot consist solely of the green light to which the eye’s image-forming visual photoreceptors are most sensitive, but must include a generous mixture of red and blue wavelengths, to which they are much less sensitive.This means that white (or whitish) light sources produce far fewer lumens per watt than the theoretical maximum of 683.002\u00a0lm\/W. The ratio between the actual number of lumens per watt and the theoretical maximum is expressed as a percentage known as the luminous efficiency. For example, a typical incandescent light bulb has a luminous efficiency of only about 2%.In reality, individual eyes vary slightly in their luminosity functions. However, photometric units are precisely defined and precisely measurable. They are based on an agreed-upon standard luminosity function based on measurements of the spectral characteristics of image-forming visual photoreception in many individual human eyes.Use in video-camera specifications[edit]Specifications for video cameras such as camcorders and surveillance cameras often include a minimal illuminance level in lux at which the camera will record a satisfactory image.[citation needed] A camera with good low-light capability will have a lower lux rating. Still cameras do not use such a specification, since longer exposure times can generally be used to make pictures at very low illuminance levels, as opposed to the case in video cameras, where a maximal exposure time is generally set by the frame rate.Non-SI units of illuminance[edit]The corresponding unit in English and American traditional units is the foot-candle. One foot candle is about 10.764\u00a0lx. Since one foot-candle is the illuminance cast on a surface by a one-candela source one foot away, a lux could be thought of as a “metre-candle”, although this term is discouraged because it does not conform to SI standards for unit names.One phot\u00a0(ph) equals 10 kilolux (10 klx).One nox\u00a0(nx) equals 1 millilux (1 mlx) at light color 2042\u00a0K or 2046\u00a0K (formerly 2360\u00a0K).[19][20][21][22]In astronomy, apparent magnitude is a measure of the illuminance of a star on the Earth’s atmosphere. A star with apparent magnitude 0 is 2.54 microlux outside the earth’s atmosphere, and 82% of that (2.08 microlux) under clear skies.[16] A magnitude 6 star (just barely visible under good conditions) would be 8.3 nanolux. A standard candle (one candela) a kilometre away would provide an illuminance of 1 microlux\u2014about the same as a magnitude 1 star.Legacy Unicode symbol[edit]Unicode includes a symbol for “lx”: U+33D3 \u33d3 SQUARE LX. It is a legacy code to accommodate old code pages in some Asian languages. Use of this code is not recommended in new documents.SI photometry units[edit]^ Standards organizations recommend that photometric quantities be denoted with a subscript “v” (for “visual”) to avoid confusion with radiometric or photon quantities. For example: USA Standard Letter Symbols for Illuminating Engineering USAS Z7.1-1967, Y10.18-1967^ The symbols in this column denote dimensions; “L“, “T” and “J” are for length, time and luminous intensity respectively, not the symbols for the units litre, tesla and joule.^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and \u03c1 for luminous efficacy of a source.See also[edit]References[edit]^ International Bureau of Weights and Measures (2019-05-20), The International System of Units (SI) (PDF) (9th\u00a0ed.), ISBN\u00a0978-92-822-2272-0, archived from the original on 2021-10-18^ CIE (2020). CIE S 017:2020 ILV: International Lighting Vocabulary, 2nd edition (2\u00a0ed.). CIE.^ ISO\/CIE 23539:2023 CIE TC 2-93 Photometry \u2014 The CIE system of physical photometry. ISO\/CIE. 2023.^ NIST Guide to SI Units. Chapter 9 \u2013 Rules and Style Conventions for Spelling Unit Names, National Institute of Standards and Technology.^ a b c d e Schlyter, Paul (1997\u20132009). “Radiometry and photometry in astronomy”.Starlight illuminance coincides with the human eye’s minimum illuminance while moonlight coincides with the human eye’s minimum colour vision illuminance (IEE Reviews, 1972, page 1183).^ Kyba, Christopher C. M.; Mohar, Andrej; Posch, Thomas (2017-02-01). “How bright is moonlight?” (PDF). Astronomy & Geophysics. 58 (1): 1.31\u20131.32. doi:10.1093\/astrogeo\/atx025.^ “Electro-Optics Handbook” (pdf). photonis.com. p.\u00a063. Retrieved 2012-04-02.[permanent dead link]^ “NOAO Common and Recommended Light Levels Indoor” (PDF). Archived from the original (PDF) on 2021-07-06. Retrieved 2016-11-13.^ a b Pears, Alan (June 1998). “Chapter 7: Appliance technologies and scope for emission reduction”. Strategic Study of Household Energy and Greenhouse Issues (PDF). Sustainable Solutions Pty Ltd. Department of Industry and Science, Commonwealth of Australia. p.\u00a061. Archived from the original (PDF) on 2011-03-02. Retrieved 2008-06-26.^ Australian Greenhouse Office (May 2005). “Chapter 5: Assessing lighting savings”. Working Energy Resource and Training Kit: Lighting. Archived from the original on 2007-04-15. Retrieved 2007-03-17.^ “Low-Light Performance Calculator”. Archived from the original on 2013-06-15. Retrieved 2010-09-27.^ Darlington, Paul (2017-12-05). “London Underground: Keeping the lights on”. Rail Engineer. Archived from the original on 2018-11-16. Retrieved 2017-12-20.^ “How to use a lux meter (Australian recommendation)” (PDF). Sustainability Victoria. April 2010. Archived from the original (PDF) on 2011-07-07.^ “Illumination. – 1926.56”. Regulations (Standards – 29 CFR). Occupational Safety and Health Administration, US Dept. of Labor. Archived from the original on 2009-05-08.^ European law UNI EN 12464^ a b Schlyter, Section 7.^ Schlyter, Section 14.^ Jack L. Lindsey, Applied Illumination Engineering, The Fairmont Press, Inc., 1997 ISBN\u00a00881732125 page 218^ Lohse, Bernhard; Stille, Ulrich [in German] (January 1948) [1947-08-19].  Written at Braunschweig, Germany.  Deutsche Physikalische Gesellschaft (ed.). “Einf\u00fchrung und Bestimmung des Licht\u00e4quivalents”. Zeitschrift f\u00fcr Physik (in German). Berlin \/ G\u00f6ttingen \/ Heidelberg, Germany: Springer-Verlag. 125 (1\u20133): 133\u2013158. doi:10.1007\/BF01337623. ISSN\u00a00044-3328. Retrieved 2023-03-19.^ Westphal, Wilhelm Heinrich (1952). “Nox, Dunkelleuchtdichte, Skot”. Physikalisches W\u00f6rterbuch (in German) (1\u00a0ed.). Berlin \/ G\u00f6ttingen \/ Heidelberg, Germany: Springer-Verlag OHG. pp.\u00a0125, 271, 389. doi:10.1007\/978-3-662-12706-3. ISBN\u00a0978-3-662-12707-0. Retrieved 2023-03-16. pp.\u00a0125, 271: Nox, abgek[\u00fcrzt] nx, Einheit der Dunkelbeleuchtungsst\u00e4rke (Dunkelleuchtdichte), welche f\u00fcr zahlenm\u00e4\u00dfige Angaben und zum Anschlu\u00df der Dunkelbeleuchtungsst\u00e4rke an die normale Beleuchtungsst\u00e4rke 1940 von der Deutschen Lichttechnischen Gesellschaft\u00a0[de] geschaffen wurde. Bez\u00fcglich der Farbtemperatur der Strahlung und des Anschlusses von Zahlenwerten der Beleuchtungsst\u00e4rke E und der Dunkelbeleuchtungsst\u00e4rke E gelten analog die gleichen Festlegungen wie bei der Dunkelleuchtdichte und dem Skot (sk). F\u00fcr eine Strahlung der Farbtemperatur T1\u00a0= 2360\u00a0K gilt: 1\u00a0nx\u00a0= 10\u22123\u00a0lx (Lux). F\u00fcr eine beliebige Strahlung bekannter spektraler Strahlungsleistung S1 lautet die Verkn\u00fcpfungsbeziehung zwischen in 10\u22123\u00a0lx gemessenem Zahlenwert {E} der Beleuchtungsst\u00e4rke und in nx gemessenem Zahlenwert {E} der Dunkelbeleuchtungsst\u00e4rke: {E}nx\u00a0= (2,161\u00a0\u00b1 0,001)\u00a0\u00b7 {E}10\u22123\u00a0lx\u00a0\u00b7 \u222b\u00a0S\u03bbV\u03bb,Wd\u03bb\u00a0\/ \u222b\u00a0S\u03bbV\u03bbd\u03bb, wobei V\u03bb die relative spektrale Hellempfindlichkeit und V\u03bb,W die relative spektrale D\u00e4mmerungsempfindlichkeit des menschlichen Auges nach Weaver[A] bedeuten. […] Dunkelleuchtdichte. […] Ist das Auge dunkeladaptiert, d.h. einer Leuchtdichte von weniger als 0,01\u00a0asb ausgesetzt, so gilt infolge des Purkinje-Ph\u00e4nomens eine von der spektralen Hellempfindlichkeitskurve abweichende, nach dem kurzwelligen Ende des Spektrums hin verschobene Empfindlichkeitskurve des Auges, die St\u00e4bchenkurve des D\u00e4mmerungssehens. Unter Zugrundelegung dieser Empfindlichkeitskurve hat man 1940 in Deutschland die Dunkelleuchtdichte mit der Einheit Skot (sk) so festgesetzt, da\u00df bei einem Licht der Farbtemperatur 2360\u00a0\u00b0K 1\u00a0sk\u00a0= 10\u22123\u00a0asb gilt. 1948 ist von der Internationalen Beleuchtungskommission (IBK) die Bezugstemperatur auf 2046\u00a0K, die Erstarrungstemperatur des Platins, festgesetzt worden. Die Bezeichnung Skot wurde von der IBK nicht \u00fcbernommen, daf\u00fcr soll “skotopisches Stilb” gesagt werden. Als h\u00f6chstzul\u00e4ssiger Grenzwert f\u00fcr die Dunkelleuchtdichte ist in Deutschland 10\u00a0Skot festgesetzt worden, um eine Verwendung der Dunkelleuchtdichte im Gebiet des gemischten Zapfen- und St\u00e4bchensehens zu vermeiden, da in diesem Bereich die photometrischen Ma\u00dfgr\u00f6\u00dfen wegen der allm\u00e4hlich gleitenden Augenempfindlichkeitskurve ihren Sinn verlieren.^ Grimsehl, Ernst [in German]; Schallreuter, Walter [in German] (1988) [1976]. “1. Licht: 1.4. Photometrie: 1.4.1. Grundbegriffe”.  In Haferkorn, Heinz (ed.). Lehrbuch der Physik: Optik (in German). Vol.\u00a03 (19\u00a0ed.). Leipzig, Germany: BSB BG Teubner Verlagsgesellschaft. pp.\u00a033\u201338 [37\u201338]. doi:10.1007\/978-3-322-96431-1. ISBN\u00a0978-3-322-96432-8. Order No. 6666211, VLN 294-375\/84\/88, LSV 1164. Retrieved 2023-03-16. pp.\u00a037\u201338: Dunkelsehen […] F\u00fcr das Dunkelsehen, bei dem nur die St\u00e4bchen angeregt werden, definiert man die Dunkelleuchtdichte mit der Einheit Skot (sk) und die Dunkelbeleuchtungsst\u00e4rke mit der Einheit Nox (nx). Die Umrechnungsfaktoren zwischen den Hell- und Dunkelgr\u00f6\u00dfen h\u00e4ngen von der spektralen Zusammensetzung des Lichtes ab. Sie werden deshalb f\u00fcr die Farbtemperatur 2042\u00a0K (fr\u00fcher 2360\u00a0K) festgelegt. Bei dieser ist 1\u00a0sk\u00a0= 10\u22123\u00a0asb und 1\u00a0nx\u00a0= 10\u22123\u00a0lx.^ Keplinger, Thomas (2021-03-29). “1939 bis 1945 \u2013 Im Keller gl\u00fcht das Lumogen”. Worte im Dunkel (in Austrian German). Vienna, Austria. Archived from the original on 2023-03-16. Retrieved 2023-03-16. Skot und Nox […] Interessant ist in diesem Zusammenhang die Einf\u00fchrung neuer Messeinheiten. Die Voraussetzungen der Forschung beziehungsweise die Erfordernisse an die Leuchtfarben unterschieden sich so stark von allen bis dahin erforschten Gebieten, dass die Deutsche Lichttechnische Gesellschaft\u00a0[de] 1940 eigene Einheiten ins Leben rief: Die Dunkelleuchtdichte wurde in Skot und die Dunkelbeleuchtungsst\u00e4rke in Nox gemessen.[B] Diese Einheiten grenzten an die bereits bestehenden Gr\u00f6\u00dfen der Leuchtdichte und Beleuchtungsst\u00e4rke an und dienten der zahlenm\u00e4\u00dfigen Erfassung geringster Lichtwerte. So entsprach etwa ein Nox 10\u22123\u00a0Lux.External links[edit]     (adsbygoogle = window.adsbygoogle || []).push({});after-content-x4"},{"@context":"http:\/\/schema.org\/","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"https:\/\/wiki.edu.vn\/en\/wiki5\/#breadcrumbitem","name":"Enzyklop\u00e4die"}},{"@type":"ListItem","position":2,"item":{"@id":"https:\/\/wiki.edu.vn\/en\/wiki5\/lux-wikipedia\/#breadcrumbitem","name":"Lux – Wikipedia"}}]}]