What is luminous efficiency? Comparison of lamps and lamps.

Measure how well a light source emits visible light

Luminous output

it is a measure of how well a light source emits visible light.
It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Depending on the context, power can be either the radiant power flow of the source, or it can be the total power (electrical, chemical, or other) consumed by the source.[1][2][3]What meaning of this term is intended should usually be inferred from context, and sometimes it's unclear. The first meaning is sometimes called the luminous efficiency of the radiation
, and the latter
the luminous efficiency of the source
or
the total luminous efficiency
.[4][5]

Not all wavelengths of light are equally visible or equally effective in stimulating human vision due to the spectral sensitivity of the human eye; Radiation in the infrared and ultraviolet parts of the spectrum are useless for lighting. The luminous efficiency of a source depends on how well it converts energy into electromagnetic radiation and how well the emitted radiation is detected by the human eye.

Luminous output of radiation

Explanation

The response of the typical human eye to light, as standardized by the CIE in 1924.
The horizontal axis represents the wavelength in nm. Wavelengths of light outside the visible spectrum are useless for lighting because they are not visible to the human eye. Moreover, the eye responds more to some wavelengths of light than others, even in the visible spectrum. This eye reaction is represented by a function of luminosity. This is a standardized function that represents the response of a “typical” eye in bright light (photopic vision). It is also possible to define a similar curve for unclear conditions (scopic vision). If nothing is specified, photopic conditions are usually assumed.

Luminous radiant efficiency measures the proportion of electromagnetic power that is used for illumination. It is obtained by dividing the luminous flux by radiant flux. Light with wavelengths outside the visible spectrum reduces luminous output because it promotes radiant flux, while the luminous flux of such light is zero. Wavelengths near the peak of the eye response contribute more than wavelengths near the edges.

The photopic luminous efficiency of radiation has a maximum possible value of 683.002 lm/W, for the case of monochromatic light at a wavelength of 555 nm (green). Scotopic luminous emission efficiency reaches a maximum of 1700 lm/W for monochromatic light at a wavelength of 507 nm.

Mathematical definition

Luminous output

, denoted
K
, is defined as[6]
K = Φ v Φ e = ∫ 0 ∞ K ( λ ) Φ e , λ d λ ∫ 0 ∞ Φ e , λ d λ , { displaystyle K = { frac { Phi _ { mathrm {v}}} { Phi _ { mathrm {e}}}} = { frac { int _ {0} ^ { infty} K ( lambda) Phi _ { mathrm {e}, lambda} , mathrm {d} lambda} { int _ {0} ^ { infty} Phi _ { mathrm {e}, lambda} , mathrm {d} lambda}},}
where

• Φv is the luminous flux;
• This is not a radiant flow;
• Φе, λ is the spectral radiant flux;
• K
  (
  λ
  ) =
  K
  m
  V
  (
  λ
  ) is the spectral luminous efficiency.

Examples

Photopic vision

Type	Luminous radiation efficiency (lm/W)	Luminous efficiency[note 1]
Tungsten incandescent lamp, standard, 2800 K	15[7]	2%
M class star (Antares, Betelgeuse), 3000 K	30	4%
Blackbody, 4000K, ideal	54.7[8]	8%
Class G star (sun, Capella), 5800 K	93[7]	13.6%
Black body, 7000 K, ideal	95[8]	14%
Blackbody, 5800 K, trimmed to 400–700 nm (ideal "white" source)[note 2]	251[7][note 3][9]	37%
Blackbody, 5800 K, truncated to ≥ 5% photopic sensitivity range[note 4]	348[9]	51%
Ideal monochrome source: 555 nm	683.002[10]	100%

Scotopic vision

Type	Luminous radiation efficiency (lm/W)	Luminous efficiency[note 1]
Ideal monochromatic 507 nm source	1699[11] or 1700[12]	100%

Spectral radiance from a black body. Energy outside the visible wavelength range (~380–750 nm, shown by gray dashed lines) reduces light output.

A simplified version of color difference thresholds. Credit: Xicato

There is also a new metric for LEDs; “color difference thresholds” (McAE). This became necessary due to the inconsistency in the color characteristics of LEDs after they come out of industrial assembly lines in the millions. The "color threshold" parameter is based on the principle of "barely noticeable difference" between LED chips. When a batch of chips has the same light output, they are classified as having the same color discrimination threshold. The greater the spread of indicators, the greater the number of color discrimination thresholds obtained.

A good manufacturer, as a rule, supplies products that have two or three color thresholds. If the stated number of thresholds exceeds six, look for another LED.

Again, as LEDs gain longevity and their color performance degrades, the number of color thresholds increases, indicating degradation of the original color rendering performance. Thus, another metric would be valuable: the deviation of the color thresholds over the nominal service life.

Lighting efficiency

Main article: Socket efficiency

Artificial light sources are usually rated in terms of the luminous efficiency of the source, also sometimes called socket efficiency

.
It is the relationship between the total luminous flux emitted by a device and the total amount of power (electrical, etc.) it consumes. The luminous output of a source is a measure of the efficiency of a device with an output power tuned to a spectral response curve (a function of luminance). Expressed in dimensionless form (for example, as a fraction of the maximum possible luminous output), this value may be called source luminous output
,
total luminous output
, or
lighting efficiency
.

The main difference between radiant luminous efficiency and source luminous efficiency is that the latter takes into account incoming energy that is lost as heat or otherwise exits the source as something other than electromagnetic radiation. Luminous radiation efficiency is a property of the radiation emitted by a source. The luminous output of a source is a property of the source as a whole.

Examples

The following table lists the source luminous output and efficiency for various light sources. Please note that all lamps requiring electrical/electronic ballast unless otherwise stated (see also voltage) are stated without penalty for this reduction in overall efficiency.

Category	Type	Overall luminous efficiency (lm/W)	Overall luminous efficiency[note 1]
Combustion	Gas mantle	1–2[13]	0.15–0.3%
Incandescent lamp	15, 40, 100 W tungsten incandescent lamp (230 V)	8.0, 10.4, 13.8[14][15][16][17]	1.2, 1.5, 2.0%
	5, 40, 100 W tungsten incandescent lamp (120 V)	5, 12.6, 17.5[18]	0.7, 1.8, 2.6%
Halogen incandescent lamp	100, 200, 500 W tungsten-halogen (230 V)	16.7, 17.6, 19.8[19][17]	2.4, 2.6, 2.9%
	2.6 W tungsten halogen (5.2 V)	19.2[20]	2.8%
	Halogen-IR (120 V)	17.7–24.5[21]	2.6–3.5%
	Tungsten Quartz Halogen (12-24V)	24	3.5%
	Photographic and projection lamps	35[22]	5.1%
Light-emitting diode	LED screw base lamp (120 V)	102[23][24][25]	14.9%
	5–16 LED lamp on screw base W (230 V)	75–120[26]	11–18%
	21.5 Modernization of W LED for fluorescent lamp T8 (230 V)	172[27]	25%
	Theoretical limit for white LED with phosphorescence color mixing	260–300[28]	38.1–43.9%
Arc lamp	Carbon arc lamp	2–7[29]	0.29–1.0%
	Xenon arc lamp	30–50[30][31]	4.4–7.3%
	Mercury-xenon arc lamp	50–55[30]	7.3–8%
	Ultra high pressure (UHP) mercury vapor arc lamp, free installation	58–78[32]	8.5–11.4%
	Ultra-high pressure mercury vapor arc lamp (UHP) with reflector for projectors	30–50[33]	4.4–7.3%
Fluorescent	32 Tube W T12 with magnetic ballast	60[34]	9%
	9–32 W compact fluorescent (with ballast)	46–75[17][35][36]	8–11.45%[37]
	T8 tube with electronic ballast	80–100[34]	12–15%
	PL-S 11 W U-pipe, excluding ballast losses	82[38]	12%
	T5 tube	70–104.2[39][40]	10–15.63%
	70–150 W electrodeless lighting system with inductive coupling	71–84[41]	10–12%
Gas release	1400 W sulfur lamp	100[42]	15%
	Metal halide lamp	65–115[43]	9.5–17%
	High pressure sodium lamp	85–150[17]	12–22%
	Low pressure sodium lamp	100–200[17][44][45]	15–29%
	Plasma display panel	2–10[46]	0.3–1.5%
Cathodoluminescence	Electron-stimulated luminescence	30–110[47][48]	15%
Ideal sources	Trimmed black body 5800 K[note 3]	251[7]	37%
	Green light at 555 nm (maximum possible luminous output by definition)	683.002[10]	100%

Sources that depend on the thermal radiation of a solid filament, such as incandescent lamps, tend to have low overall efficiency because, as Donald L. Klipstein explained, "an ideal thermal emitter emits visible light most efficiently at about 6300 °C (6600 K or 11500°F). Even at such a high temperature, a lot of radiation is infrared or ultraviolet, and the theoretical luminous [efficiency] is 95 lumens per watt. Neither substance is solid and can be used as a light bulb filament at temperatures close to this. the surface of the sun is not that hot."[22] At temperatures where the tungsten filament of a conventional light bulb remains solid (below 3683 kelvin), most of its radiation is in the infrared.[22]

Customizable white colors

Something that has recently become important is the color performance of “tunable white sources.” These are multi-channel LED light sources where the white light settings can be shifted between “warm” and “cool” temperatures. What is rarely pointed out is the effect on color rendering when going across the entire range. Ideally, changing color temperatures will follow the "ideal emitter" curve over the corresponding color temperature range. There will be lighting systems for which this information will be extremely important.

SI photometric units

SI photometric quantities

• v
• T
• e

Quantity		Unit		Measurement	Notes
Name	Symbol[nb 1]	Name	Symbol	Symbol
Light energy	Q v[No. 3]	second lumen	⋅s	T J	The clear second is sometimes called a talbot .
Luminous flux, luminous intensity	Φ [№ 3]	lumen (= candela steradians)	lm (= cd⋅sr)	J	Light energy per unit time
Light intensity	i v	candela (= lumens per steradian)	(=lm/sr)	J	Luminous flux per unit solid angle
Brightness	Lv _	candela per square meter	cd/m2 (= lm/(sr⋅m2))	L −2 J	Luminous flux per unit solid angle per unit projected source area. The candela per square meter is sometimes called the nit .
Illumination	Ev _	lux (= lumens per square meter)	(=lm/m2)	L −2 J	Luminous flux incident on the surface
Luminous efficacy, luminous flux	Mv _	lumen per square meter	lm/m2	L −2 J	Luminous flux is emitted from the surface
Light exposure	HOUR v	luxury second	lx	L −2 T J	Time-integrated illuminance
Light energy density	ωv _	lumen second per cubic meter	lm⋅s/m3	L −3 T J
Luminous output (radiation)	K	lumen per watt	lm /	M −1 L −2 T 3 J	Ratio of luminous flux to radiant flux
Luminous output (source)	η [№ 3]	lumen per watt	lm /	M −1 L −2 T 3 J	Ratio of luminous flux to power consumption
Luminous efficacy, luminous coefficient	V	1	Luminous output normalized to the maximum possible luminous output
See also: · Photometry · Radiometry

1. Standards organizations recommend denoting photometric quantities with the suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities. For example: US Standard Letter Symbols for Lighting Engineering
   USAS Z7.1-1967, Y10.18-1967
2. The symbols in this column indicate dimensions; " L
   ", "
   T
   " and "
   J
   " represent length, time and luminous intensity respectively, rather than symbols for the units liter, tesla and joule.
3. ^ a b c
   Alternative symbols are sometimes found:
   W
   for luminous energy,
   n
   or
   F
   for luminous flux, and
   ρ
   for luminous output of the source.

What does it depend on

In theory, it is believed that this data should only relate to the light source itself and in no way affect the entire luminaire.

However, practice shows that a huge contribution to the final result of luminous efficiency is made by:

• several spotlights

• speaker shape

• driver

• LED temperature mode

• uniform measurement conditions

Therefore, it would be more correct to call this term “light output of a lamp.” When purchasing, always ask about this parameter, for example, what is the power of a group of lighting fixtures, and not its LEDs inside.

Notes

1. ^ a b c
   Determined in such a way that the maximum possible luminous
   efficiency
   corresponds to a luminous
   efficiency
   of 100%.
2. The most effective source that simulates the solar spectrum within the limits of human visual sensitivity.
3. ^ a b
   Integral of the truncated Planck function times photopeak luminosity function times 683.002 lm/W.
4. Omits the part of the spectrum where eye sensitivity is low (≤ 5% of the peak).

Recommendations

1. Allen Stimson (1974). Photometry and Radiometry for Engineers
   . New York: Wiley and Son.
2. Frank Groom; Richard Becherer (1979). Optical Radiation Measurements, Volume 1
   . New York: Academic Press.
3. Robert Boyd (1983). Radiometry and optical radiation detection
   . New York: Wiley and Son.
4. Roger A. Messenger; Jerry Ventre (2004). Photovoltaic Systems Engineering
   (2nd ed.). CRC Press. item 123. ISBN 978-0-8493-1793-4.
5. Eric Reinhard; Erum Arif Khan; Ahmet Oguz Akyuz; Garrett Johnson (2008). Color Imaging: Fundamentals and Applications
   . A. K. Peters, LLC p.338. ISBN 978-1-56881-344-8.
6. "Luminous efficacy (radiation)." CIE. Retrieved 2016-06-07.
7. ^ a b c d
   “Maximum white light efficiency” (PDF). Retrieved 2011-07-31.
8. ^ a b
9. ^ a b
   Murphy, Thomas W. (2012).
   "Maximum spectral luminous efficiency of white light." Journal of Applied Physics
   .
   111
   (10):104909–104909–6. arXiv:1309.7039. Bibcode:2012JAP...111j4909M. doi:10.1063/1.4721897. S2CID 6543030.
10. ^ a b
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11. Kohei Narisada; Duco Schreuder (2004). Handbook of Light Pollution
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    .
    New York: Civic Press. 22
    (5): 490.
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15. "Philips Classictone Standard 40W, clear."
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17. ^ a b c d f
    Philips Product Catalog (German)
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22. ^ a b c
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28. White LEDs with ultra-high luminous efficiency Physorg.com
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30. ^ a b
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32. REVIEW ARTICLE: UHP Lamps for Projection Applications[ permanent dead link
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34. ^ a b
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