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Buena Vista Social Club - Candela
Buena Vista Social Club - Candela
Published: 2010/09/10
Channel: Canal De Salsa
LA VERDAD DE YAO CABRERA Y EL VIRAL TEAM *pruebas*
LA VERDAD DE YAO CABRERA Y EL VIRAL TEAM *pruebas*
Published: 2017/09/20
Channel: Candela Diaz
Buena Vista Social Club - Candela
Buena Vista Social Club - Candela
Published: 2009/11/25
Channel: finelylaw
De La Ghetto - Candela ft. Willy Cultura [Official Audio]
De La Ghetto - Candela ft. Willy Cultura [Official Audio]
Published: 2016/05/15
Channel: De La Ghetto
Me vas a extrañar - Orquesta Candela VIDEO OFICIAL  4k
Me vas a extrañar - Orquesta Candela VIDEO OFICIAL 4k
Published: 2016/11/28
Channel: Orquesta Candela
EL FIN DE YAO CABRERA *Candela Diaz*
EL FIN DE YAO CABRERA *Candela Diaz*
Published: 2017/09/21
Channel: RenzoCenationn
De La Ghetto - Candela ft. Willy Cultura
De La Ghetto - Candela ft. Willy Cultura
Published: 2016/05/24
Channel: GanjaMusicHD
Chayanne - Candela
Chayanne - Candela
Published: 2009/10/03
Channel: chayanneVEVO
LA VERDAD De Dos Bros, Yao Cabrera AMENAZA a Candela Diaz! - VIRAL TEAM ¿Es Puras MENTIRAS?
LA VERDAD De Dos Bros, Yao Cabrera AMENAZA a Candela Diaz! - VIRAL TEAM ¿Es Puras MENTIRAS?
Published: 2017/09/20
Channel: xMauriiPvP
AHORA ME LLAMA KAROL G - Candela Diaz (cover)
AHORA ME LLAMA KAROL G - Candela Diaz (cover)
Published: 2017/08/21
Channel: Candela Diaz
Candela Diaz REVELÓ La VERDAD de YAO CABRERA y el VIRAL TEAM | *RIP Dos bros* | AGUANTE DOSOGAS
Candela Diaz REVELÓ La VERDAD de YAO CABRERA y el VIRAL TEAM | *RIP Dos bros* | AGUANTE DOSOGAS
Published: 2017/09/21
Channel: iDanirex - ImDani_
Papá Kumbe - Candela
Papá Kumbe - Candela
Published: 2017/08/21
Channel: Jorge Jimenez
No me mientas  Jerry Rivera y Orquesta Candela Oficial
No me mientas Jerry Rivera y Orquesta Candela Oficial
Published: 2014/12/09
Channel: Orquesta Candela
Magneto & Mercurio - Candela (En Vivo)
Magneto & Mercurio - Candela (En Vivo)
Published: 2016/06/17
Channel: MagnetoMercurioVEVO
Orquesta Candela - Domingos de fiesta 2017  CONCIERTO EN VIVO FULL HD
Orquesta Candela - Domingos de fiesta 2017 CONCIERTO EN VIVO FULL HD
Published: 2017/04/08
Channel: Orquesta Candela
Culcha Candela - Monsta
Culcha Candela - Monsta
Published: 2015/02/12
Channel: CulchaCandelaVEVO
Noelia - Candela
Noelia - Candela
Published: 2006/04/19
Channel: Michel Alamilla
Yo nunca ft. @celiaahemmings
Yo nunca ft. @celiaahemmings
Published: 2017/09/22
Channel: Candela Sartorius
Noelia - Candela
Noelia - Candela
Published: 2011/04/06
Channel: DiscomaniChannel
SE REVELÓ CANDELA *El fin de Yao Cabrera*
SE REVELÓ CANDELA *El fin de Yao Cabrera*
Published: 2017/09/20
Channel: JUAMPI 2
LA VERDAD DE YAO CABRERA Y EL VIRALTEAM | RESUMIDO - CANDELA DIAZ
LA VERDAD DE YAO CABRERA Y EL VIRALTEAM | RESUMIDO - CANDELA DIAZ
Published: 2017/09/21
Channel: YagomTM
Malak - Candela feat. I-Nesta (Video Oficial)
Malak - Candela feat. I-Nesta (Video Oficial)
Published: 2017/02/27
Channel: Music Hit Factory
VideoClip Oficial - CANDELA 1989 - Stan MC
VideoClip Oficial - CANDELA 1989 - Stan MC
Published: 2016/06/20
Channel: StanMC
SOY PEOR BAD BUNNY - Candela Diaz (cover)
SOY PEOR BAD BUNNY - Candela Diaz (cover)
Published: 2017/09/03
Channel: Candela Diaz
Popurri del grupo Bryndis - La Pura Candela
Popurri del grupo Bryndis - La Pura Candela
Published: 2016/09/30
Channel: La Pura Candela
esta noche orquesta candela  video clip oficial
esta noche orquesta candela video clip oficial
Published: 2012/04/04
Channel: orquesta candela de victor yaipen
La candela, brillant pour terminer - SI - 07
La candela, brillant pour terminer - SI - 07
Published: 2017/08/19
Channel: e-penser
DICAS IMPORTANTES SOBRE A CANDELA! | COLUNA DOS CASTERS | BLOOD ORCHID
DICAS IMPORTANTES SOBRE A CANDELA! | COLUNA DOS CASTERS | BLOOD ORCHID
Published: 2017/09/21
Channel: Ubisoft e-Sports - BRASIL
MORENA SON - Candela
MORENA SON - Candela
Published: 2012/09/27
Channel: Radio Gladys Palmera
Rosario Tijeras-Yo soy Candela letra
Rosario Tijeras-Yo soy Candela letra
Published: 2016/12/30
Channel: • Monserrat •
What is One CANDELA  (Luminous intensity)
What is One CANDELA (Luminous intensity)
Published: 2016/06/09
Channel: Makrani Education
Paco Candela - El Niño y El Vagabundo (Oficial)
Paco Candela - El Niño y El Vagabundo (Oficial)
Published: 2016/12/29
Channel: Senador Música
Culcha Candela - Rodeo (Offizielles Musikvideo)
Culcha Candela - Rodeo (Offizielles Musikvideo)
Published: 2017/07/13
Channel: CulchaCandelaVEVO
Juan Alcaraz vs Daddy Yankee - Candela
Juan Alcaraz vs Daddy Yankee - Candela
Published: 2017/03/14
Channel: Juan Alcaraz Music
Culcha Candela - Von allein
Culcha Candela - Von allein
Published: 2013/10/02
Channel: CulchaCandelaVEVO
Culcha Candela - Cool mit mir selbst (Offizielles Musikvideo) ft. Ela
Culcha Candela - Cool mit mir selbst (Offizielles Musikvideo) ft. Ela
Published: 2017/08/21
Channel: CulchaCandelaVEVO
ORQUESTA CANDELA | ME VAS A EXTRAÑAR ( Domingos de Fiesta - TV Perú )
ORQUESTA CANDELA | ME VAS A EXTRAÑAR ( Domingos de Fiesta - TV Perú )
Published: 2016/12/21
Channel: MMUSIC PERU
LA CUMBIA CANDELA SONIDO ZEUS SAN PABLO DEL MONTE TLAXCALA
LA CUMBIA CANDELA SONIDO ZEUS SAN PABLO DEL MONTE TLAXCALA
Published: 2017/09/21
Channel: RICHARD TV
Te Amo Para Siempre Orquesta Candela - Vídeo Oficial (4K)
Te Amo Para Siempre Orquesta Candela - Vídeo Oficial (4K)
Published: 2016/12/04
Channel: Orquesta Candela
Paco Candela - Seguire siendo de campo (Oficial)
Paco Candela - Seguire siendo de campo (Oficial)
Published: 2017/05/24
Channel: Senador Música
Sueña - Orquesta Candela by Danilo
Sueña - Orquesta Candela by Danilo
Published: 2008/10/11
Channel: Danny Siccha
LA CUMBIA CANDELA \\ SONIDO SAMURAI \\ PLAZA LOS GALLOS 6 DE MAYO 2017
LA CUMBIA CANDELA \\ SONIDO SAMURAI \\ PLAZA LOS GALLOS 6 DE MAYO 2017
Published: 2017/05/09
Channel: Sonideros en Movimiento TV
Vente pa`aca` maria oyo rojo llamo a radio candela
Vente pa`aca` maria oyo rojo llamo a radio candela
Published: 2017/08/30
Channel: video de todo lo mejor
Crimen de Candela: Perpetua para Bermúdez y Jara
Crimen de Candela: Perpetua para Bermúdez y Jara
Published: 2017/09/20
Channel: Todo Noticias
Grupo Femenino Candela - No me vuelvo a enamorar
Grupo Femenino Candela - No me vuelvo a enamorar
Published: 2014/05/14
Channel: Hnos. CHOQUECHAMBI
Maia - Candela
Maia - Candela
Published: 2009/07/24
Channel: Canal youtube
No te vayas - Orquesta Candela y Ráfaga Oficial
No te vayas - Orquesta Candela y Ráfaga Oficial
Published: 2015/06/02
Channel: Orquesta Candela
MENTIRAS ORQUESTA CANDELA  oficial
MENTIRAS ORQUESTA CANDELA oficial
Published: 2013/04/13
Channel: Orquesta Candela
CANDELA DÍAZ Y EL EDITOR ENMASCARADO HABLAN DE LA VERDAD DE YAO CABRERA Y EL VIRAL TEAM
CANDELA DÍAZ Y EL EDITOR ENMASCARADO HABLAN DE LA VERDAD DE YAO CABRERA Y EL VIRAL TEAM
Published: 2017/09/20
Channel: YERRY
Duo Candela - hace un año ya
Duo Candela - hace un año ya
Published: 2011/10/03
Channel: Carlos Mellace
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WIKIPEDIA ARTICLE

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Candela
Luminosity.png
Photopic (black) and scotopic[1] (green) luminosity functions. The photopic includes the CIE 1931 standard[2] (solid), the Judd–Vos 1978 modified data[3] (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data[4] (dotted). The horizontal axis is wavelength in nm.
Unit information
Unit system SI base unit
Unit of Luminous intensity
Symbol cd 
Linear visible spectrum.svg

The candela (/kænˈdɛlə/ or /kænˈdlə/; symbol: cd) is the SI base unit of luminous intensity; that is, luminous power per unit solid angle emitted by a point light source in a particular direction. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the standard luminosity function (a model of the sensitivity of the human eye to different wavelengths).[4][5] A common candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured.

The word candela means candle in Latin.

Definition[edit]

Like most other SI base units, the candela has an operational definition—it is defined by a description of a physical process that will produce one candela of luminous intensity. Since the 16th General Conference on Weights and Measures (CGPM) in 1979, the candela has been defined as:[6]

The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The definition describes how to produce a light source that (by definition) emits one candela. Such a source could then be used to calibrate instruments designed to measure luminous intensity.

The candela is sometimes still called by the old name candle,[7] such as in foot-candle and the modern definition of candlepower.

Explanation[edit]

The frequency chosen is in the visible spectrum near green, corresponding to a wavelength of about 555 nanometres. The human eye is most sensitive to this frequency, when adapted for bright conditions. At other frequencies, more radiant intensity is required to achieve the same luminous intensity, according to the frequency response of the human eye. The luminous intensity for light of a particular wavelength λ is given by

where Iv(λ) is the luminous intensity in candelas, lm is short for lumen, W for watt, Ie(λ) is the radiant intensity in W/sr and is the standard luminosity function (photopic). If more than one wavelength is present (as is usually the case), one must sum or integrate over the spectrum of wavelengths present to get the total luminous intensity.

Examples[edit]

  • A common candle emits light with roughly 1 cd luminous intensity.
  • A 25 W compact fluorescent light bulb puts out around 1700 lumens; if that light is radiated equally in all directions (i.e. 4π steradians), it will have an intensity of .
  • Focused into a 20° beam, the same light bulb would have an intensity of around 18,000 cd.
  • The luminous intensity of light-emitting diodes is measured in millicandelas (mcd), or thousandths of a candela. Indicator LEDs are typically in the 50 mcd range; "ultra-bright" LEDs can reach 15,000 mcd (15 cd), or higher.

Origin[edit]

Prior to 1948, various standards for luminous intensity were in use in a number of countries. These were typically based on the brightness of the flame from a "standard candle" of defined composition, or the brightness of an incandescent filament of specific design. One of the best-known of these was the English standard of candlepower. One candlepower was the light produced by a pure spermaceti candle weighing one sixth of a pound and burning at a rate of 120 grains per hour. Germany, Austria and Scandinavia used the Hefnerkerze, a unit based on the output of a Hefner lamp.[8]

It became clear that a better-defined unit was needed. Jules Violle had proposed a standard based on the light emitted by 1 cm2 of platinum at its melting point (or freezing point), calling this the Violle. The light intensity was due to the Planck radiator (a black body) effect, and was thus independent of the construction of the device. This made it easy for anyone to measure the standard, as high-purity platinum was widely available and easily prepared.

The Commission Internationale de l'Éclairage (International Commission on Illumination) and the CIPM proposed a “new candle” based on this basic concept. However, the value of the new unit was chosen to make it similar to the earlier unit candlepower by dividing the Violle by 60. The decision was promulgated by the CIPM in 1946:

The value of the new candle is such that the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimetre.[9]

It was then ratified in 1948 by the 9th CGPM which adopted a new name for this unit, the candela. In 1967 the 13th CGPM removed the term "new candle" and gave an amended version of the candela definition, specifying the atmospheric pressure applied to the freezing platinum:

The candela is the luminous intensity, in the perpendicular direction, of a surface of 1 / 600 000 square metre of a black body at the temperature of freezing platinum under a pressure of 101 325 newtons per square metre.[10]

In 1979, because of the difficulties in realizing a Planck radiator at high temperatures and the new possibilities offered by radiometry, the 16th CGPM adopted the modern definition of the candela.[11] The arbitrary (1/683) term was chosen so that the new definition would exactly match the old definition. Although the candela is now defined in terms of the second (an SI base unit) and the watt (a derived SI unit), the candela remains a base unit of the SI system, by definition.[12]

SI photometric light units[edit]

SI photometry quantities
Quantity Unit Dimension Notes
Name Symbol[nb 1] Name Symbol Symbol
Luminous energy Qv [nb 2] lumen second lm⋅s TJ [nb 3] Units are sometimes called talbots.
Luminous flux / luminous power Φv [nb 2] lumen (= cd⋅sr) lm J [nb 3] Luminous energy per unit time.
Luminous intensity Iv candela (= lm/sr) cd J [nb 3] Luminous flux per unit solid angle.
Luminance Lv candela per square metre cd/m2 L−2J Luminous flux per unit solid angle per unit projected source area. Units are sometimes called nits.
Illuminance Ev lux (= lm/m2) lx L−2J Luminous flux incident on a surface.
Luminous exitance / luminous emittance Mv lux lx L−2J Luminous flux emitted from a surface.
Luminous exposure Hv lux second lx⋅s L−2TJ
Luminous energy density ωv lumen second per cubic metre lm⋅s⋅m−3 L−3TJ
Luminous efficacy η [nb 2] lumen per watt lm/W M−1L−2T3J Ratio of luminous flux to radiant flux or power consumption, depending on context.
Luminous efficiency / luminous coefficient V 1
See also: SI · Photometry · Radiometry
  1. ^ Standards organizations recommend that photometric quantities be denoted with a suffix "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
  2. ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
  3. ^ a b c "J" here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.

Relationships between luminous intensity, luminous flux, and illuminance[edit]

If a source emits a known luminous intensity Iv (in candelas) in a well-defined cone, the total luminous flux Φv in lumens is given by

Φv = Iv 2π [1 − cos(A/2)],

where A is the radiation angle of the lamp—the full vertex angle of the emission cone. For example, a lamp that emits 590 cd with a radiation angle of 40° emits about 224 lumens. See MR16 for emission angles of some common lamps.[13][14]

If the source emits light uniformly in all directions, the flux can be found by multiplying the intensity by 4π: a uniform 1 candela source emits 12.6 lumens.

For the purpose of measuring illumination, the candela is not a practical unit, as it only applies to idealized point light sources, each approximated by a source small compared to the distance from which its luminous radiation is measured, also assuming that it is done so in the absence of other light sources. What gets directly measured by a light meter is incident light on a sensor of finite area, i.e. illuminance in lm/m2 (lux). However, if designing illumination from many point light sources, like light bulbs, of known approximate omnidirectionally-uniform intensities, the contributions to illuminance from incoherent light being additive, it is mathematically estimated as follows. If ri is the position of the i-th source of uniform intensity Ii, and â is the unit vector normal to the illuminated elemental opaque area dA being measured, and provided that all light sources lie in the same half-space divided by the plane of this area,

In the case of a single point light source of intensity Iv, at a distance r and normally incident, this reduces to

See also[edit]

References[edit]

  1. ^ CIE Scotopic luminosity curve (1951)
  2. ^ CIE (1931) 2-deg color matching functions
  3. ^ Judd–Vos modified CIE 2-deg photopic luminosity curve (1978)
  4. ^ a b Sharpe, Stockman, Jagla & Jägle (2005) 2-deg V*(l) luminous efficiency function Archived 27 September 2007 at the Wayback Machine.
  5. ^ Wyzecki, G.; Stiles, W.S. (1982). Color Science: Concepts and Methods, Quantitative Data and Formulae (2nd ed.). Wiley-Interscience. ISBN 0-471-02106-7. 
  6. ^ "Base unit definitions: Candela". The NIST Reference on Constants, Units, and Uncertainty. Retrieved 27 September 2010. 
  7. ^ Merriam-Webster
  8. ^ "Hefner unit, or Hefner candle". Sizes.com. 30 May 2007. Retrieved 25 February 2009. 
  9. ^ Barry N. Taylor (1992). The Metric System: The International System of Units (SI). U. S. Department of Commerce. p. 18. ISBN 0-941375-74-9.  (NIST Special Publication 330, 1991 ed.)
  10. ^ 13th CGPM Resolution 5, CR, 104 (1967), and Metrologia, 4, 43–44 (1968).
  11. ^ 16th CGPM Resolution 3, CR, 100 (1979), and Metrologia, 16, 56 (1980).
  12. ^ "The photometric base unit – the candela" (pdf). SI Brochure. Bureau International des Poids et Mesures. 7 September 2007. 
  13. ^ Theory
  14. ^ Online converter

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