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Buena Vista Social Club - Candela
Buena Vista Social Club - Candela
Published: 2010/09/10
Channel: Canal De Salsa
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
Buena Vista Social Club - Candela
Buena Vista Social Club - Candela
Published: 2009/11/25
Channel: finelylaw
Chayanne - Candela
Chayanne - Candela
Published: 2009/10/03
Channel: chayanneVEVO
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
FEDE VIGEVANI y CANDELA DIAZ son NOVIOS? **¿FADELA ES REAL?** | DOSOGAS
FEDE VIGEVANI y CANDELA DIAZ son NOVIOS? **¿FADELA ES REAL?** | DOSOGAS
Published: 2017/11/24
Channel: iDanirex
Malak feat. Fyahbwoy & I-Nesta - Candela (Remix) [Vídeo Oficial]
Malak feat. Fyahbwoy & I-Nesta - Candela (Remix) [Vídeo Oficial]
Published: 2017/10/10
Channel: Music Hit Factory
"Maldita Traición"  Orquesta Candela Video Oficial  4K
"Maldita Traición" Orquesta Candela Video Oficial 4K
Published: 2017/11/05
Channel: Orquesta Candela
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
De La Ghetto - Candela ft. Willy Cultura
De La Ghetto - Candela ft. Willy Cultura
Published: 2016/05/24
Channel: GanjaMusicHD
Noelia - Candela
Noelia - Candela
Published: 2006/04/19
Channel: Michel Alamilla
MORENA SON - Candela
MORENA SON - Candela
Published: 2012/09/27
Channel: Radio Gladys Palmera
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
Probando dulces japoneses con mi abuela
Probando dulces japoneses con mi abuela
Published: 2017/11/09
Channel: Candela Sartorius
Rosario Tijeras-Yo soy Candela letra
Rosario Tijeras-Yo soy Candela letra
Published: 2016/12/30
Channel: • Monserrat •
Magneto & Mercurio - Candela (En Vivo)
Magneto & Mercurio - Candela (En Vivo)
Published: 2016/06/17
Channel: MagnetoMercurioVEVO
Popurri del grupo Bryndis - La Pura Candela
Popurri del grupo Bryndis - La Pura Candela
Published: 2016/09/30
Channel: La Pura Candela
The Italian town Candela will pay for living there
The Italian town Candela will pay for living there
Published: 2017/10/21
Channel: Sehar Tv
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: TotalMusic PERÚ
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
Quand Candela a chambré Di Biagio
Quand Candela a chambré Di Biagio
Published: 2017/11/16
Channel: Volmog 16
Maia - Candela
Maia - Candela
Published: 2009/07/24
Channel: Canal youtube
Les souvenirs de Vincent Candela sur la goal machine Gabriel Batistuta
Les souvenirs de Vincent Candela sur la goal machine Gabriel Batistuta
Published: 2017/11/16
Channel: Volmog 16
Papá Kumbe - Candela
Papá Kumbe - Candela
Published: 2017/08/21
Channel: Jorge Jimenez
David Deseo ft New Class - CANDELA (Videoclip Official)
David Deseo ft New Class - CANDELA (Videoclip Official)
Published: 2017/10/06
Channel: David Deseo
esta noche orquesta candela  video clip oficial
esta noche orquesta candela video clip oficial
Published: 2012/04/04
Channel: orquesta candela de victor yaipen
Culcha Candela - Rodeo (Offizielles Musikvideo)
Culcha Candela - Rodeo (Offizielles Musikvideo)
Published: 2017/07/13
Channel: CulchaCandelaVEVO
Los Cadillac
Los Cadillac's - Candela
Published: 2014/11/10
Channel: LosCadillacsVEVO
BUYA - CANDELA
BUYA - CANDELA
Published: 2015/11/08
Channel: Buya Espiritu Bueno
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
MENTIRAS ORQUESTA CANDELA  oficial
MENTIRAS ORQUESTA CANDELA oficial
Published: 2013/04/13
Channel: Orquesta Candela
ORQUESTA CANDELA MIX 2016  PROVINCIANO CUMBIARETO CABALLO VIEJO
ORQUESTA CANDELA MIX 2016 PROVINCIANO CUMBIARETO CABALLO VIEJO
Published: 2016/04/25
Channel: luisito8870
VideoClip Oficial - CANDELA 1989 - Stan MC
VideoClip Oficial - CANDELA 1989 - Stan MC
Published: 2016/06/20
Channel: StanMC
Paco Candela - Seguire siendo de campo (Oficial)
Paco Candela - Seguire siendo de campo (Oficial)
Published: 2017/05/24
Channel: Senador Música
Paco Candela - El Niño y El Vagabundo (Oficial)
Paco Candela - El Niño y El Vagabundo (Oficial)
Published: 2016/12/29
Channel: Senador Música
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
ANGUSTIA orquesta Candela - Oficial
ANGUSTIA orquesta Candela - Oficial
Published: 2013/09/06
Channel: Orquesta Candela
Noelia - Candela
Noelia - Candela
Published: 2011/04/06
Channel: DiscomaniChannel
Duo Candela - hace un año ya
Duo Candela - hace un año ya
Published: 2011/10/03
Channel: Carlos Mellace
AHORA ME LLAMA KAROL G - Candela Diaz (cover)
AHORA ME LLAMA KAROL G - Candela Diaz (cover)
Published: 2017/08/21
Channel: Candela Diaz
Juan Alcaraz vs Daddy Yankee - Candela
Juan Alcaraz vs Daddy Yankee - Candela
Published: 2017/03/14
Channel: Juan Alcaraz Music
Sueña - Orquesta Candela by Danilo
Sueña - Orquesta Candela by Danilo
Published: 2008/10/11
Channel: Danny Siccha
A 6 años del crimen de Candela, nuevos detalles
A 6 años del crimen de Candela, nuevos detalles
Published: 2017/06/01
Channel: Todo Noticias
PACO CANDELA FANDANGO DEL NIÑO GLORIA,POR REBOLLO,UNOS NATURALES Y EL TEMA DE SO.S.
PACO CANDELA FANDANGO DEL NIÑO GLORIA,POR REBOLLO,UNOS NATURALES Y EL TEMA DE SO.S.
Published: 2013/04/26
Channel: Paco Candela
Paco Candela 2016. Siéntate a mi vera.12.
Paco Candela 2016. Siéntate a mi vera.12.
Published: 2016/01/05
Channel: _Quique_
No te vayas - Orquesta Candela y Ráfaga Oficial
No te vayas - Orquesta Candela y Ráfaga Oficial
Published: 2015/06/02
Channel: Orquesta Candela
"MIX MUSICAL CON LA ORQUESTA CANDELA" Orquesta Candela  (DOMINGOS DE FIESTA TV PERÚ HD)
"MIX MUSICAL CON LA ORQUESTA CANDELA" Orquesta Candela (DOMINGOS DE FIESTA TV PERÚ HD)
Published: 2015/09/11
Channel: David Correa Arévalo
PARRANDA CABALLO VIEJO ORQUESTA CANDELA 2015
PARRANDA CABALLO VIEJO ORQUESTA CANDELA 2015
Published: 2014/11/27
Channel: Orquesta Candela
Candela - Amame (HD) Tinku 2016
Candela - Amame (HD) Tinku 2016
Published: 2016/01/23
Channel: RonconBolivia
Yerba buena - la candela (prendela) ft. Orishas
Yerba buena - la candela (prendela) ft. Orishas
Published: 2011/03/27
Channel: André Cuba
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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 base unit of luminous intensity in the International System of Units (SI); 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 wax 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] The lumen second is sometimes called the talbot.
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. The candela per square metre is sometimes called the nit.
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 Time-integrated illuminance
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 Luminous efficacy normalized by the maximum possible efficacy
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 joule.

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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