luminous efficacy - wikipedia

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Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminousflux to power. Depending on context, the power can be either the radiant flux of the source's output, or it can

be the total power (electric power, chemical energy, or others) consumed by the source. [1][2][3] Which sense

of the term is intended must usually be inferred from the context, and is sometimes unclear. The former sense is sometimes called luminous efficacy of radiation , and the latter luminous efficacy of a source .

The luminous efficacy of a source is a measure of the efficiency with which the source provides visible lightfrom electricity. [4] The luminous efficacy of radiation describes how well a given quantity of electromagnetic radiation from a source produces visible light: the ratio of luminous flux to radiant flux. [5]

Not all wavelengths of light are equally visible, or equally effective at stimulating human vision, due to thespectral sensitivity of the human eye; radiation in the infrared and ultraviolet parts of the spectrum is uselessfor illumination. The overall luminous efficacy of a source is the product of how well it converts energy toelectromagnetic radiation, and how well the emitted radiation is detected by the human eye.

1 Efficacy and efficiency2 Luminous efficacy of radiation

2.1 Explanation2.2 Mathematical definition2.3 Examples

2.3.1 Photopic vision2.3.2 Scotopic vision

3 Lighting efficiency3.1 Examples

4 SI photometry units5 See also6 Notes7 References8 External links

In some systems of units, luminous flux has the same units as radiant flux. The luminous efficacy of radiation is then dimensionless. In this case, it is often instead called the luminous efficiency , and may beexpressed as a percentage. A common choice is to choose units such that the maximum possible efficacy,683 lm/W, corresponds to an efficiency of 100%. The distinction between efficacy and efficiency is notalways carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed inlumens per watt, or "efficacies" expressed as a percentage.

The luminous coefficient is luminous efficiency expressed as a value between zero and one, with onecorresponding to an efficacy of 683 lm/W.

inous efficacy - Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Luminous_efficacy

9 01-Jun-16 17:17



The response of a typical human eyeto light, as standardized by the CIE in1924. The horizontal axis iswavelength in nm

Explanation

Wavelengths of light outside of the visible spectrum are not usefulfor illumination because they cannot be seen by the human eye.Furthermore, the eye responds more to some wavelengths of lightthan others, even within the visible spectrum. This response of theeye is represented by the luminosity function. This is a standardized

function which represents the response of a "typical" eye under bright conditions (photopic vision). One can also define a similar curve for dim conditions (scotopic vision). When neither is specified,

photopic conditions are generally assumed.

Luminous efficacy of radiation measures the fraction of electromagnetic power which is useful for lighting. It is obtained bydividing the luminous flux by the radiant flux. Light withwavelengths outside the visible spectrum reduces luminous efficacy,

because it contributes to the radiant flux while the luminous flux of such light is zero. Wavelengths near the peak of the eye's response contribute more strongly than those near the edges.

In SI, luminous efficacy has units of lumens per watt (lm/W). Photopic luminous efficacy of radiation has amaximum possible value of 683 lm/W, for the case of monochromatic light at a wavelength of 555 nm(green). Scotopic luminous efficacy of radiation reaches a maximum of 1700 lm/W for narrowband light of wavelength 507 nm.

Mathematical definition

The dimensionless luminous efficiency measures the integrated fraction of the radiant power that contributes

to its luminous properties as evaluated by means of the standard luminosity function. [6] The luminouscoefficient is

where

yλ is the standard luminosity function, J λ is the spectral power distribution of the radiant intensity.

The luminous coefficient is unity for a narrow band of wavelengths at 555 nanometres.

Note that is an inner product between and and that is the one-norm of .

Examples

Photopic vision


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Type Luminous efficacy of

radiation(lm/W)

Luminousefficiency [note 1]

Typical tungsten light bulb at 2800 K 15 [7] 2%

Class M star (Antares, Betelgeuse), 3000 K 30 4%

Ideal black-body radiator at 4000 K 54.7[8]

8%Class G star (Sun, Capella), 5800 K 93 [7] 13.6%

Ideal black-body radiator at 7000 K 95 [8] 14%

Ideal 5800 K black-body, truncated to 400–700 nm(ideal "white" source) [note 2] 251 [7][note 3][9] 37%

5800 K black-body truncated to ≥2% photopicsensitivity range [note 4] 292 [10][9] 43%

2800 K black-body truncated to ≥2% photopic

sensitivity range [note 4] 299[10][9]

44%



Ideal monochromatic 555 nm source 683 [11] 100%

Scotopic vision

Type Luminous efficacy of radiation(lm/W)

Luminous efficiency [note 1]

Ideal monochromatic 507 nm source 1699 lm/W [12] or 1700 lm/W [13] 100%


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Spectral radiance of a black body. Energy outsidethe visible wavelength range (~380–750 nm, shown

by grey dotted lines) reduces the luminousefficiency.

Artificial light sources are usually evaluated in terms of luminous efficacy of a source, also sometimescalled overall luminous efficacy . This is the ratio between the total luminous flux emitted by a device andthe total amount of input power (electrical, etc.) it consumes. It is also sometimes referred to as thewall-plug luminous efficacy or simply wall-plug efficacy . The overall luminous efficacy is a measure of the efficiency of the device with the output adjusted to account for the spectral response curve (the

“luminosity function”). When expressed in dimensionless form (for example, as a fraction of the maximum possible luminous efficacy), this value may be called overall luminous efficiency , wall-plug luminousefficiency , or simply the lighting efficiency .

The main difference between the luminous efficacy of radiation and the luminous efficacy of a source is thatthe latter accounts for input energy that is lost as heat or otherwise exits the source as something other thanelectromagnetic radiation. Luminous efficacy of radiation is a property of the radiation emitted by a source.Luminous efficacy of a source is a property of the source as a whole.

Examples

The following table lists luminous efficacy of a source and efficiency for various light sources. Note that alllamps requiring electrical/electronic ballast are unless noted (see also voltage) listed without losses for that,reducing total efficiency.


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Category Type Overall

luminousefficacy (lm/W)

Overallluminous

efficiency [note 1]

Combustioncandle 0.3 [note 6] 0.04%

gas mantle 1–2 [14] 0.15–0.3%

Incandescent

100–200 W tungsten incandescent(230 V) 13.8 [15] –15.2 [16] 2–2.2%

100–200–500 W tungsten glass halogen(230 V)

16.7 [17] –17.6 [16] – 19.8 [16] 2.4–2.6–2.9%

5–40–100 W tungsten incandescent(120 V) 5–12.6 [18] –17.5 [18] 0.7–1.8–2.6%

2.6 W tungsten glass halogen (5.2 V) 19.2 [19] 2.8%

tungsten quartz halogen (12–24 V) 24 3.5%

photographic and projection lamps 35 [20] 5.1%

Light-emitting diode

white LED (raw, without power supply)4.5–150 [21][22]

[23][24] 0.66–22%

4.1 W LED screw base lamp (120 V) 58.5–82.9 [25] 8.6–12%

5.4 W LED screw base lamp (100 V50/60 Hz) 101.9 [26] 14.9%

6.9 W LED screw base lamp (120 V) 55.1–81.9 [25] 8.1–12%

7 W LED PAR20 (120 V) 28.6[27]

4.2%7 W LED PAR30 (110-230 V) 60 [28] 8.8%

8.7 W LED screw base lamp (120 V) 69–93.1 [25][29] 10.1–13.6%

Theoretical limit for a white LED with phosphorescence color mixing 260–300 [30] 38.1–43.9%

Arc lamp

carbon arc lamp 2-7 [31] 0.29-1.0%

xenon arc lamp 30–50 [32][33] 4.4–7.3%

mercury-xenon arc lamp50–55

[32] 7.3–8%

UHP – ultra-high-pressuremercury-vapor arc lamp: initial, freemounted

58–78 [34] 8.5–11.4%

UHP – ultra-high-pressuremercury-vapor arc lamp: rated, withreflector for projectors

30–50 [35] 4.4–7.3%

Fluorescent

very low pressure mercury-vapor gas-discharge lamp with fluorescence as

T12 tube with magnetic ballast

60 [36] 9%

9–32 W compact fluorescent (with ballast) 46–75 [16][37][38] 8–11.45% [39]


9 01-Jun-16 17:17



Category Type Overall

luminousefficacy (lm/W)

Overallluminous

efficiency [note 1]

T8 tube with electronic ballast 80–100 [36] 12–15%

PL-S 11 W U-tube, excluding ballastloss 82 [40] 12%

T5 tube 70–104.2 [41][42] 10–15.63%

70-150W Inductively CoupledElectrodeless Lighting System 71-84 [43] 10-12%

Gas discharge

1400 W sulfur lamp 100 [44] 15%

metal halide lamp 65–115 [45] 9.5–17%

high pressure sodium lamp 85–150 [16] 12–22%

low pressure sodium lamp 100–200 [16][46][47] 15–29%

Plasma display panel 2-10 [48] 0.3–1.5%

Cathodoluminescence electron stimulated luminescence 30 5%

Ideal sourcesTruncated 5800 K blackbody [note 3] 251 [7] 37%

Green light at 555 nm (maximum possible luminous efficacy) 683.002 [11] 100%

Sources that depend on thermal emission from a solid filament, such as incandescent light bulbs, tend tohave low overall efficacy because, as explained by Donald L. Klipstein, “An ideal thermal radiator produces

visible light most efficiently at temperatures around 6300 °C (6600 K or 11,500 °F). Even at this hightemperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous [efficacy] is95 lumens per watt. No substance is solid and usable as a light bulb filament at temperatures anywhere closeto this. The surface of the sun is not quite that hot.” [20] At temperatures where the tungsten filament of anordinary light bulb remains solid (below 3683 kelvins), most of its emission is in the infrared. [20]


9 01-Jun-16 17:17



Quantity Unit DimensionNotes

Name Symbol [nb 1] Name Symbol Symbol

Luminous energy Qv[nb 2] lumen second lm⋅s T ⋅J [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.

Luminousintensity

I vcandela(= lm/sr)

cd J [nb 3] Luminous power per unit solidangle.

Luminance Lvcandela per square metre cd/m 2 L −2⋅J

Luminous power per unit solidangle per unit projected sourcearea. Units are sometimes callednits .

Illuminance E v lux (= lm/m 2) lx L −2⋅JLuminous power incident on asurface.

Luminousexitance /luminousemittance

M v lux lx L −2⋅JLuminous power emitted from asurface.

Luminousexposure

H v lux second lx⋅s L −2⋅T ⋅J

Luminous energydensity

ω v

lumen second per cubicmetre

lm⋅s⋅m−3 L −3⋅T ⋅J

Luminousefficacy η [nb 2] lumen per

wattlm/W M −1⋅L −2⋅T 3⋅J

Ratio of luminous flux to radiantflux or power consumption,depending on context.

Luminousefficiency /luminouscoefficient

V 1

See also: SI · Photometry · Radiometry

Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") toavoid confusion with radiometric or photon quantities. For example: USA Standard Letter Symbols for

Illuminating Engineering USAS Z7.1-1967, Y10.18-1967

1.

Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminousefficacy.

2.

"J " here is the symbol for the dimension of luminous intensity, not the symbol for the unit joules.3.

Photometry

Light pollutionWall-plug efficiency – a related principle, but slightly differentCoefficient of utilizationList of light sources


9 01-Jun-16 17:17



OSRAM Sylvania Lamp and Ballast Catalog . 2007.33.REVIEW ARTICLE: UHP lamp systems for projection applications (http://www.koti.mbnet.fi/jahonen/Electronics/Stuff/UHP_Lamp.pdf) Journal of Physics D: Applied Physics

34.

OSRAM P-VIP PROJECTOR LAMPS (http://www.beamerlampen.biz/EASYLAMP_OSRAM_VIP_Projector_Lamp.pdf) Osram

35.

Federal Energy Management Program (December 2000). "How to buy an energy-efficient fluorescent tube lamp".U.S. Department of Energy.

36.

"Low Mercury CFLs". Energy Federation Incorporated. Archived from the original on October 13, 2008.

Retrieved 2008-12-23.

37.

"Conventional CFLs". Energy Federation Incorporated. Archived from the original on October 14, 2008.Retrieved 2008-12-23.

38.

"Global bulbs". 1000Bulbs.com. Retrieved 2010-2-20. Check date values in: | access- dat e= (help)|39.Phillips. "Phillips Master". Retrieved 2010-12-21.40.Department of the Environment, Water, Heritage and the Arts, Australia. "Energy Labelling—Lamps". Archivedfrom the original on July 23, 2008. Retrieved 2008-08-14.

41.

"BulbAmerica.com". Bulbamerica.com. Archived from the original on December 1, 2012. Retrieved 2010-02-20.42.SYLVANIA. "SYLVANIA ICETRON® QUICKTRONIC® Design Guide" (PDF) . Retrieved 2015-06-10.43."1000-watt sulfur lamp now ready". IAEEL newsletter (1) (IAEEL). 1996. Archived from the original on2003-08-18.

44.

"The Metal Halide Advantage". Venture Lighting . 2007. Retrieved 2008-08-10.45."LED or Neon? A scientific comparison".46."Why is lightning coloured? (gas excitations)". webexhibits.org.47."Future Looks Bright for Plasma TVs" (PDF) . Panasonic. 2007. Retrieved 2013-02-10.48.

Hyperphysics has these graphs of efficacy (http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html#c2) that do not quite comply with the standard definitionEnergy Efficient Light Bulbs (http://www.cus.net/electricity/subcats/eleclighting.html)

Other Power (http://www.otherpower.com/otherpower_lighting.html)

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