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Encyclopedia > Luminous efficacy

Luminous efficacy is a property of light sources, which indicates what portion of the emitted electromagnetic radiation is usable for human vision. It is the ratio of emitted luminous flux to radiant flux. Luminous efficacy is related to the overall efficiency of a light source for illumination, but the overall lighting efficiency also depends on how much of the input energy is converted into electromagnetic waves (whether visible or not). Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye, or in a more general sense, any electromagnetic radiation in the range from infrared to ultraviolet. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... This does not cite any references or sources. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... Luminous flux or luminous power is the measure of the perceived power of light. ... This article does not cite any references or sources. ... Lighting includes both artificial light sources such as lamps and natural illumination of interiors from daylight. ...

The response of a typical human eye to light. The horizontal axis is wavelength in nm.
The response of a typical human eye to light. The horizontal axis is wavelength in nm.

Contents

Image File history File links Download high-resolution version (1300x975, 94 KB) CIE 1931 luminosity function File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Luminous efficacy Photopic vision ... Image File history File links Download high-resolution version (1300x975, 94 KB) CIE 1931 luminosity function File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Luminous efficacy Photopic vision ...

Explanation

Wavelengths of light outside of the visible spectrum are not useful for illumination because they cannot be seen by the human eye. Furthermore, the eye responds more to some wavelengths of light than others, even within the visible spectrum. This response of the eye 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 not specified, photopic conditions are generally assumed. The wavelength is the distance between repeating units of a wave pattern. ... The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. ... This article refers to the sight organ. ... The luminosity function is a standard function established by the Commission Internationale de lÉclairage to account for the variable sensitivity of the human eye to radiation at different wavelengths. ... Photopic vision is the vision of the light-adapted eye; in many animals, color vision, mediated by cone cells. ... Scotopic vision is the monochromatic vision of the eye in dim light. ...


Luminous efficacy measures the fraction of electromagnetic power which is useful for lighting. It is obtained by dividing the luminous flux by the radiant flux. Light with wavelengths outside the visible spectrum does not contribute to the efficacy at all, because 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. Luminous flux is a measure of the energy emitted by a light source in all directions. ... Luminous flux or luminous power is the measure of the perceived power of light. ... The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. ...


In SI, luminous efficacy has units of lumens per watt (lm/W). Photopic luminous efficacy has a maximum possible value of 683 lm/W, for the case of monochromatic light at a wavelength of 555 nm (green). Scotopic luminous efficacy reaches a maximum of 1700 lm/W for narrowband light of wavelength 507 nm. Look up si, Si, SI in Wiktionary, the free dictionary. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ...


Efficacy and efficiency

In some other systems of units, luminous flux has the same units as radiant flux. The luminous efficacy is then dimensionless. In this case, it is often instead called the luminous efficiency or luminous coefficient and may be expressed as a percentage. For example, it is common to express the luminous efficiency in units where the maximum possible efficacy, 683 lm/W, corresponds to an efficiency of 100%. The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage. The former Weights and Measures office in Middlesex, England. ... In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement...


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.[1] The luminosity coefficient is In calculus, the integral of a function is an extension of the concept of a sum. ... In photometry, Luminous flux or luminous power is the measure of the perceived power of light. ... The luminosity function is a standard function established by the Commission Internationale de lÉclairage to account for the variable sensitivity of the human eye to radiation at different wavelengths. ...

frac{ int^{lambda = infin}_{lambda = 0} y_lambda J_lambda dlambda } { int^{lambda = infin}_{lambda = 0} J_lambda dlambda },

where

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

The luminous coefficient is unity for a narrow band of wavelengths at 555 nanometres. The spectral power distribution (SPD) of a light source is a measurement of the energy output at points (usually 31) along the visible spectrum. ... A nanometre (American spelling: nanometer, symbol nm) is a unit of length in the metric system, equal to one thousand-millionth of a metre, which is the current SI base unit of length. ...


Examples

Type
 		 Luminous efficacy
(lm/W)		 Luminous efficiency[2]
 
Class M star (Antares, Betelgeuse), 3000 K 30 4%
ideal black-body radiator at 4000 K 47.5 [3] 7.0%
Class G star (Sun, Capella), 5800 K 80 12%
natural sunlight 93 14%
ideal black-body radiator at 7000 K 95 [3] 14%
ideal white light source 242.5 [4] 35.5%
ideal monochromatic 555 nm source 683 [5] 100%

This article or section does not cite its references or sources. ... Betelgeuse (Alpha (α) Orionis) is a semiregular variable star located 427 light-years away [1]. It is the second brightest star in the constellation Orion, and the ninth brightest star in the night sky. ... WMAP image of the cosmic microwave background radiation anisotropy. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... Capella (α Aur / α Aurigae / Alpha Aurigae) is the brightest star in the constellation Auriga and sixth brightest star in the sky. ... Prism splitting light High Resolution Solar Spectrum Sunlight in the broad sense is the total spectrum of the electromagnetic radiation given off by the Sun. ...

Lighting efficiency

Artificial light sources are usually evaluated in terms of a related quantity, the overall luminous efficacy. This is the ratio between the total luminous flux emitted by a device and the total amount of input power (electrical, etc.) it consumes. This is often simply called "luminous efficacy", which can be confusing as it also has units of lm/W. 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, or simply the lighting efficiency.


The main difference between the regular and "overall" efficacies is that the latter account for input energy that is lost as heat or otherwise exits the source as something other than electromagnetic radiation. True luminous efficacy is a property of the radiation emitted by a source. Overall luminous efficacy is a property of the source as a whole. For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another as a result of a difference in temperature. ...


Examples

The following table lists overall luminous efficacy and efficiency for various light sources:

Category
 		 Type
 		 Overall
luminous efficacy (lm/W)		 Overall
luminous efficiency[2]
Combustion candle 0.3 [6] 0.04%
Incandescent 5 W tungsten incandescent 5 0.7%
40 W tungsten incandescent 12.6 [7] 1.9%
100 W tungsten incandescent 17.5 [7] 2.6%
glass halogen 16 2.3%
quartz halogen 24 3.5%
high-temperature incandescent 35 [4] 5.1%
Fluorescent 5–24 W compact fluorescent 45–60 [8] 6.6%–8.8%
34 W fluorescent tube (T12) 50 7%
32 W fluorescent tube (T8) 60 9%
36 W fluorescent tube (T8) up to 93 up to 14%
28 W fluorescent tube (T5) 104 15.2%
Light-emitting diode white LED 26–70 [9][10] 3.8%–10.2%
white LED (prototypes) up to 150 [11][12][13] up to 22%
Arc lamp xenon arc lamp 30–50 4.4%–7.3%
mercury-xenon arc lamp 50–55 [14] 7.3%–8.0%
Gas discharge high pressure sodium lamp 150 [15] 22%
low pressure sodium lamp 183 [15] up to 200 [16] 27%
1400 W sulfur lamp 100 15%
Theoretical maximum
(monochromatic 540x1012 Hz,
approx. 555 nm, green)		 683.002 100%

Sources that depend on thermal emission from a solid filament, such as incandescent light bulbs, tend to have low overall efficacy compared to an ideal blackbody source 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 high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous efficiency [sic] is 95 lumens per watt. Of course, nothing known to any humans is solid and usable as a light bulb filament at temperatures anywhere close to this. The surface of the sun is not quite that hot."[4] At temperatures where the tungsten filament of an ordinary light bulb remains solid (below 3683 kelvin), most of its emission is in the infrared. This article needs additional references or sources for verification. ... An incandescent lamp bulb and its glowing filament. ... Fluorescent lamps in Shinbashi, Tokyo, Japan Assorted types of fluorescent lamps. ... Blue, green and red LEDs. ... 15 kW Xenon short-arc lamp. ... 15 kW Xenon short-arc lamp used in IMAX projectors Xenon arc lamps are an artificial light source. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Standard atomic weight 200. ... General Name, Symbol, Number xenon, Xe, 54 Chemical series noble gases Group, Period, Block 18, 5, p Appearance colorless Standard atomic weight 131. ... Gas discharge lamps are a family of artificial light sources that generate light by sending an electric current through a special gas. ... A LPS / SOX streetlight at full power A sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. ... A LPS / SOX streetlight at full power A sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. ... LBNL researcher examines prototype sulfur lamp. ... An incandescent lamp bulb and its glowing filament. ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Standard atomic weight 183. ... Image of two girls in mid-infrared (thermal) light (false-color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ...


SI photometry units

[edit]

SI photometry units
Quantity Symbol SI unit Abbr. Notes
Luminous energy Qv lumen second lm·s units are sometimes called talbots
Luminous flux F lumen (= cd·sr) lm also called luminous power
Luminous intensity Iv candela (= lm/sr) cd an SI base unit
Luminance Lv candela per square metre cd·m-2 units are sometimes called nits
Illuminance Ev lux (= lm/m2) lx Used for light incident on a surface
Luminous emittance Mv lux (= lm/m2) lx Used for light emitted from a surface
Luminous efficacy   lumen per watt lm·W-1 ratio of luminous flux to radiant flux; maximum possible is 683.002

Look up si, Si, SI in Wiktionary, the free dictionary. ... luminous energy : visible radiant energy, visible light ; units are lumen*seconds or Talbots (T = lm*s) ; lumen = candela*steradian ... The lumen (symbol: lm) is the SI unit of luminous flux. ... Look up second in Wiktionary, the free dictionary. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... Look up second in Wiktionary, the free dictionary. ... In photometry the Talbot (T) is a nonstandard unit of luminous energy. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... Luminous intensity is a measure of the energy emitted by a light source in a particular direction. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... The SI system of units defines seven SI base units: physical units defined by an operational definition. ... Luminance (also called luminosity) is a photometric measure of the density of luminous intensity in a given direction. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... This article is about the unit of measure. ... Illuminance is the total luminous flux incident per unit area. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... In photometry, illuminance is the total luminous flux incident on a surface, per unit area. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... The lux (symbol: lx) is the SI derived unit of illuminance or illumination. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ... The lumen (symbol: lm) is the SI unit of luminous flux. ... The watt (symbol: W) is the SI derived unit of power, equal to one joule per second. ... Luminous flux is a measure of the energy emitted by a light source in all directions. ... Luminous flux or luminous power is the measure of the perceived power of light. ...

See also

The luminous coefficient is a coefficient that measures the integrated fraction of the radiant power that contributes to its luminous properties as evaluated by means of the standard luminosity function. ... In astronomy, photometry is the measurement of the flux or intensity of an astronomical objects electromagnetic radiation. ... This time exposure photo of New York City shows sky glow, one form of light pollution. ...

References

  1. ^ (January 1958) Van Nostrand's Scientific Encyclopedia, 3rd Edition. Princeton, New Jersey, Toronto, London, New York: D. Van Nostrand Company, Inc.. 
  2. ^ a b Defined such that the maximum value possible is 100%.
  3. ^ a b Black body visible spectrum
  4. ^ a b c Klipstein, Donald L. (1996). The Great Internet Light Bulb Book, Part I. Retrieved on 2006-04-16.
  5. ^ See luminosity function.
  6. ^ 1 candela*4π steradians/40 W
  7. ^ a b http://physics.ccri.cc.ri.us/keefe/light.htm. Retrieved on 2003-02-13. Referenced page is no longer available.
  8. ^ China energy saving lamp. Retrieved on 2006-04-16.
  9. ^ Klipstein, Donald L.. The Brightest and Most Efficient LEDs and where to get them. Don Klipstein's Web Site. Retrieved on 2006-04-16.
  10. ^ Cree launches the new XLamp 7090 XR-E Series Power LED, the first 160-lumen LED!.
  11. ^ Improving White LED Efficiency Through Scattered Photon Extraction. Rensselaer Polytechnic Institute. Retrieved on 2006-04-19.
  12. ^ Cree Demonstrates 131 Lumens per Watt White LED. Cree, Inc. Press Release (2006-06-20). Retrieved on 2006-12-03.
  13. ^ Nichia Corp. claims white LED delivering 150 lumens/Watt efficiency. Nichia Corp. Press Release (2006-12-22). Retrieved on 2006-12-03.
  14. ^
  15. ^ a b LED or Neon? A scientific comparison.
  16. ^ Why is lightning coloured? (gas excitations).

For the Manfred Mann album, see 2006 (album). ... April 16 is the 106th day of the year in the Gregorian calendar (107th in leap years). ... The luminosity function is a standard function established by the Commission Internationale de lÉclairage to account for the variable sensitivity of the human eye to radiation at different wavelengths. ... Photopic (black) and scotopic [1] (green) luminosity functions. ... The steradian (ste from Greek stereos, solid) is the SI derived unit of solid angle, and the 3-dimensional equivalent of the radian. ... Year 2003 (MMIII) was a common year starting on Wednesday (link displays 2003 calendar) of the Gregorian calendar. ... is the 44th day of the year in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... April 16 is the 106th day of the year in the Gregorian calendar (107th in leap years). ... For the Manfred Mann album, see 2006 (album). ... April 16 is the 106th day of the year in the Gregorian calendar (107th in leap years). ... For the Manfred Mann album, see 2006 (album). ... April 19 is the 109th day of the year in the Gregorian calendar (110th in leap years). ... For the Manfred Mann album, see 2006 (album). ... is the 171st day of the year (172nd in leap years) in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... is the 337th day of the year (338th in leap years) in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... December 22 is the 356th day of the year (357th in leap years) in the Gregorian calendar. ... For the Manfred Mann album, see 2006 (album). ... is the 337th day of the year (338th in leap years) in the Gregorian calendar. ...

External links


  Results from FactBites:
 
Luminous efficacy - Wikipedia, the free encyclopedia (664 words)
Luminous efficacy is the ratio of the total apparent power of a light source to its actual total power.
Luminous efficacy measures the fraction of power which is useful for lighting.
The luminous coefficient is unity for a narrow band of wavelengths at 555 nanometres.
Luminous energy - Wikipedia, the free encyclopedia (173 words)
In photometry, luminous energy is the perceived energy of light.
Luminous energy is not the same as the radiant energy, the corresponding objective physical quantity.
The SI unit of luminous energy is the lumen second, which is unofficially known as the Talbot in honor of William Henry Fox Talbot.
  More results at FactBites »

 

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