Luminous efficiency is the ratio of luminous flux to power consumption. It is measured in lumens per watt (lm/w).

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.

Gas discharge lamps

The physical basis of the glow is an electrical discharge passing through a gas hermetically sealed in a tube.

Depending on the internal contents of the tube, the following types are distinguished:

Mercury:
DID;
luminescent;
Sodium.
Neon, xenon, argon, etc.

The glow process must be started using a special ballast mechanism (PRM). Currently, luminaires are produced in which the PRM can be either built into the socket or mounted separately.

Mercury

All mercury-containing devices are highly toxic and require disposal through hazardous waste collection points. In accordance with the Minamata Convention on Mercury, the production, export and import of certain mercury-containing lamps will be prohibited from 2020, along with a similar ban for mercury-containing batteries and thermometers.

DRL lamp (mercury arc fluorescent)

A high-pressure mercury lamp should not be used in rooms where people stay for a long time (apartments, offices).

These lighting devices find their application in street lighting, in automated industrial workshops, and in agriculture.

Minuses:

Low Ra: 40 – 59.
Long switching time (up to 15 minutes), depending on the ambient temperature (the colder it is, the longer the illumination process takes).
The tube gets very hot.
Sensitivity to voltage changes: with frequent short-term power outages, the device will go out, and then, after being turned on again, return to operating mode for a long time.

Classic DRLs are gradually falling out of use.

Currently, combined type devices are produced for household use (for example, by OSRAM).

DRI lamp (mercury arc lamp with emitting additives)

Also called metal halide.

DRL lamps, into the bulb of which halides of certain metals (sodium, indium, etc.) are added.

Base E27, E40, R7S (base with recessed contact, used primarily in high-intensity lighting installations, after marking the base the length of the bulb is indicated in mm - 78 or 118):

Base	E27, E40, R7S
Power	20 – 2000 W
Luminous output	70–95 lm/W
Color rendering Ra	more than 90
Light temperature	3500 – 6000 K
Price	from 500 rub.
Life time	8,000 – 10,000 hours

Mercury-quartz lamps (PRK, DRT)

Arc high-pressure heat pumps of the DRT type (arc mercury tubular, obsolete - direct mercury-quartz, PRT) are used in medical equipment (that is, quartz cabinets) for disinfecting air and products. DRTs are also used in some technological processes (such as photopolymerization).

Fluorescent lamps

Or, in other words, fluorescent lamps.

The marking of domestic devices indicates the emission spectrum:

Marking	Hue
LB	white
LD	day
LE	natural
LHB	cold
LTB	warm

After the letter markings there are numbers: the first indicates the degree of color rendering (the higher it is, the more natural the light looks, range 6–9), the next two indicate the color temperature:

30 (3000 K) – warm white;
35 (3500 K) – white;
40 (4000 K) – cool white;
54 (5400 K) – daylight;
65 (6500 K) – cold daytime;

A G-base is used, which is a socket into which the cylinder is attached using pins. Used for halogen and fluorescent compact lamps (to reduce dimensions). There are a large number of markings for this type of base, so each time it is necessary to compare the type of fastening (it is indicated on the bulb); the bases are not interchangeable.

Pros:

Low operating temperature (safe to touch).
Soft light.
Operating time up to 30,000 hours.
Modern compact models can be connected to a regular socket (fluorescent lighting devices of the previous generation were made in the form of tubes and required the use of special cylinders for their connection).

Minuses:

The operation of the source is not silent (the glow process is accompanied by a hum).
Plus operating ambient temperatures.
Toxicity - requires disposal to special landfills (free for the population through hazardous waste collection points).
A fairly long switching period during which the light reaches its maximum.
Sensitivity to frequent on-off switching.

From the listed features it is clear that it is advisable to install such equipment in places where it is necessary to provide illumination for a long time with a minimum number of switches. For example, on the first floors of stairs.

If the mode of use involves a short period of operation with frequent switching on (for example, in bathrooms), it is better to choose another source.

Characteristics:

Base	G
Power	4 – 140 W
Luminous output	40–90 lm/W
Color rendering Ra	from 60 to more than 90 (for various types)
Light temperature	3000 – 6000 K
Price	from 100 rub.
Life time	30,000 h.

Sodium lamps

Sodium vapor discharge lamps

These lamps produce monochrome yellow light. They are used where a high color rendering index is not required: in street and road lighting, for illumination of buildings, etc. High pressure lamps (HPL) are used in agriculture for additional illumination of plants in winter.

There are several markings for domestically produced sodium arc (NA) light sources:

DNaT – tubular DN;
DNaS - DN in a light-scattering flask, are a replacement for DRL;
DNaMT – frosted;
DNaZ – mirror;

Base	E27, E40
Power	50 – 100 W
Light outputNLND (low pressure)NLHD	200 lm/W150 lm/W
Color rendering Ra	from less than 39 to 59
Light temperature	3000 – 6000 K
Price	from 200 rub.
Life time	30,000 h.

Xenon lamps

Allows you to get very good color rendition.

They are used in car headlights, as well as in projectors, flashlights and other lighting devices.

Depending on the application, their price varies from several hundred to several thousand rubles. They have a highly specialized purpose.

Characteristics:

Base	N (special base for xenon)
Luminous output	50 – 90 lm/W
Color rendering Ra	OK. 100
Light temperature	3000 – 12,000 K
Price	from 200 rub.
Life time	3000

Neon, argon, etc.

Gas discharge lamps, the bulb of which is filled with an inert gas.

They have a long service life (up to 80,000 hours), and depending on the composition of the gas mixture, they make it possible to obtain light sources of various shades (from blue-green to red-orange). Used for advertising lighting and to indicate network voltage.

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%
Incandescent lamp	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%
Ideal sources	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]

Comparison of lamps

Here are the luminous output data for different light sources:

incandescent lamp - from 10 to 12 Lumens / Watt

fluorescent lamps (but only from quality manufacturers) - from 50 to 80 Lumens / Watt

Sodium gas discharge lamp NL, has a very good indicator - about 200 Lumens / W

lED - record efficiency - up to 300 Lumens / Watt

However, 300Lm/W is just a laboratory result, not a mass product.

Luminous efficiency in energy saving is the most important parameter. And the entire evolution of lamp development actually comes down to achieving its theoretical limit values of 683 lm / W.

Even if, to be realistic, even values of 500 lm/W are physically unattainable today.

SI photometric units

SI photometric quantities

Quantity		Unit		Measurement	Notes
Name	Symbol[nb 1]	Name	Symbol	Symbol	Notes
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

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
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.
^ 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.

Light intensity is the main indicator

Luminous intensity refers to one of the primary characteristics of any emitter in a specified optical range. It determines exactly how much power is transferred in certain directions, limited by a conventional solid angle. Therefore, in a graphical image, the luminous intensity configuration will not appear as a straight line.

The vertex of the solid angle is located at the center of the sphere. The unit of measurement for this angle is the steradian. To calculate it, you need to correlate the area of an imaginary ball with the square of the radius. Therefore, the steradian is a dimensionless quantity, like the solid angle itself. According to the definition, the area of a sphere fits 12.56 steradians or 4 Pi.

A solid angle is three-dimensional and looks like a cone, the vertex of which is located in the center of an imaginary ball. However, its base cannot be considered a plane, so a comparison of a solid angle and a cone will not be entirely correct. The part of the sphere that is cut off by the side surface is considered as the base. However, it should be noted that light intensity is used extremely rarely for practical calculations. Instead, they began to use such an integral parameter as luminous flux, the value of which is applied to all labels of lighting devices.

Notes

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

Notes[edit]

^B installed in such a way that the maximum possible luminous efficiency
corresponds to a luminous
efficiency
of 100%.
The most effective source that simulates the solar spectrum within the limits of human visual sensitivity.
^ab Integral of the truncated Planck function multiplied by the photopic luminosity function multiplied by 683.002 lm/W.
^ ab Excludes the part of the spectrum in which the sensitivity of the eye is very low.
^ ab Passes through that part of the spectrum where the sensitivity of the eye is low (≤ 5% of the peak).

Recommendations

Allen Stimson (1974). Photometry and Radiometry for Engineers
. New York: Wiley and Son.
Frank Groom; Richard Becherer (1979). Optical Radiation Measurements, Volume 1
. New York: Academic Press.
Robert Boyd (1983). Radiometry and optical radiation detection
. New York: Wiley and Son.
Roger A. Messenger; Jerry Ventre (2004). Photovoltaic Systems Engineering
(2nd ed.). CRC Press. item 123. ISBN 978-0-8493-1793-4.
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.
"Luminous efficacy (radiation)." CIE. Retrieved 2016-06-07.
^ a b c d
“Maximum white light efficiency” (PDF). Retrieved 2011-07-31.
^ a b
^ 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.
^ a b
"BIPM Statement: Information for Users on the Proposed Revision of the SI" (PDF). Archived (PDF) from the original January 21, 2022. Retrieved May 5, 2022.
Kohei Narisada; Duco Schreuder (2004). Handbook of Light Pollution
. Springer. ISBN 1-4020-2665-X.
Casimer DeCusatis (1998). Handbook of Applied Photometry
. Springer. ISBN 1-56396-416-3.
Westermeyer, F. W. (1920). "Recent Developments in Gas Street Lighting." American city
.
New York: Civic Press. 22
(5): 490.
"Philips Classictone Standard 15W, clear."
"Philips Classictone Standard 40W, clear."
"Lamps: Gluehbirne.ch: Philips standard lamps (in German)." Bulbs.ch. Retrieved 2013-05-17.
^ a b c d f
Philips Product Catalog (German)
Keefe, T.J. (2007). "The Nature of Light". Archived from the original on 01/2012/18. Retrieved 2016-04-15.
Osram Halogen (PDF). osram.de
(in German). Archived from the original (PDF) on November 7, 2007. Retrieved 2008-01-28.
"Osram 6406330 Miniwatt-Halogen 5.2V." Bulbtronics.com. Archived from the original on 2016-02-13. Retrieved 2013-04-16.
"GE Lighting HIR Plus Halogen PAR38s" (PDF). ge.com. Retrieved 2017-11-01.
^ a b c
Klipstein, Donald L. (1996). "The Great Online Light Bulb Book, Part I." Archived from the original on 2001-09-09. Retrieved 2006-04-16.
"Toshiba E-CORE LED lamp." item.rakuten.com. Retrieved 2013-05-17.
"Toshiba E-CORE LDA5N-E17 LED lamp." Archived from the original on July 19, 2011.
Toshiba to release 93 lm/W Ledrevie LED lamp
"Philips - LED lamps." Received 2020-03-14.
"MAS LEDtube 1500mm UE 21.5W 840 T8." Received 2018-01-10.
White LEDs with ultra-high luminous efficiency Physorg.com
"Arc lamps". Edison Technical Center. Retrieved 2015-08-20.
^ a b
"Technical information about lamps" (PDF).
Optical building blocks
. Retrieved 2010-05-01. Please note that the 150 lm/W value for xenon lamps is a typo. There is other useful information on the page.
Catalog of lamps and ballasts OSRAM Sylvania
. 2007.
REVIEW ARTICLE: UHP Lamps for Projection Applications[ permanent dead link
] Journal of Physics D: Applied Physics
OSRAM P-VIP PROJECTOR LAMPS Osram
^ a b
Federal Energy Management Program (December 2000). “How to buy an energy-efficient fluorescent lamp.” US Department of Energy. Archived from the original on 2007-07-02. Magazine citation required | log = (help)
“Low mercury CFL.” Energy Federation Incorporated. Archived from the original on October 13, 2008. Retrieved 2008-12-23.
"Regular CFLs." Energy Federation Incorporated. Archived from the original on October 14, 2008. Retrieved 2008-12-23.
"Global Bulbs". 1000Bulbs.com. Retrieved 2010-02-20.|
Phillips. Phillips Master. Retrieved 2010-12-21.
Department of Environment, Water, Heritage and the Arts, Australia. "Energy labeling - lamps." Archived from the original on July 23, 2008. Retrieved 2008-08-14.CS1 maint: multiple names: list of authors (link)
BulbAmerica.com. Bulbamerica.com. Archived from the original on December 1, 2012. Retrieved 2010-02-20.
SYLVANIA. "Sylvania Icetron Quicktronic Design Guide" (PDF). Retrieved 2015-06-10.
“The 1000 W sulfur lamp is ready.” IAEEL Newsletter
(1). IAEEL. 1996. Archived from the original on August 18, 2003.
"The Advantage of Metal Halides". Venture Lighting
. 2007. Archived from the original on 2012-02-17. Retrieved 2008-08-10.
“LED or neon? Scientific comparison".
“Why is the lightning colored? (Gas excitation).” webexhibits.org.
"The future looks bright for plasma TVs" (PDF). Panasonic. 2007. Retrieved 2013-02-10.
"TV-Tube Technology Creates an Efficient Light Bulb." OSA. 2019. Retrieved 2020-09-12.
Sheshin, Evgeniy P.; Kolodyazhny, Artem Y.; Chadaev Nikolay N.; Getman Alexander Olegovich; Danilkin, Mikhail I.; Ozol, Dmitry Ivanovich (2019). "Prototype cathodoluminescent lamp for general lighting with field emission carbon fiber cathode." Journal of Vacuum Science and Technology
B.
AVS. 37
(3): 031213. doi:10.1116/1.5070108. Retrieved 2020-09-12.

Luminous radiation efficiency

Glow efficiency is measured as the ratio of luminous power (Lm) to the electrical power of the source (W). The Lm/W ratio is an indicator of the efficiency of a lighting source. With equal electrical energy consumption, LED lamps emit a more powerful luminous flux compared to incandescent lamps. The emission efficiency of LEDs is much higher compared to conventional light bulbs. For example, the brightness of an 8 W LED is approximately equal to the brightness of a 40 W incandescent lamp. Thus, LED lamps allow you to save energy without compromising the brightness of the lighting.

What photometric quantities are used in lighting calculations

Due to ingrained habit, many continue to believe that the assessment of room illumination can be done in energy units - watts. This misconception is easily explained - we are left with this persistent stereotype as a legacy from the times of complete dominance of incandescent lamps.

Incandescent lamps were produced with different power consumption - 15, 25, 40, 60, 75, 100, 150 and more watts. And every owner of a house or apartment knew from his own experience that for normal lighting in the living room, for example, he must screw three 60-watt bulbs into a chandelier, a “forty” will be enough for a table lamp, a hundred-watt one for the kitchen, etc.

By the way, a clear legacy of this is still the practice used by lamp manufacturers - to indicate on their packaging, in addition to power consumption, luminous efficiency expressed in the equivalent power of old incandescent lamps.

So let's remember the first thing - neither the luminous flux emitted by a lamp nor the surface illumination resulting from it is measured in watts. The watts indicated on the body of the device are the amount of electricity consumed by the lamp, which, through certain physical transformations, is converted into visible light.

Some people of the older generation are generally sure that the luminous output of a lighting device is measured in candles. By the way, this is not so far from the truth, and why will become clear below. But again, this is not illumination at all.

So it makes sense to consider the main photometric quantities in order, from the light source to the illuminated surface. Let’s make a reservation right away – this topic is quite difficult for an unprepared person to understand. Therefore, we will try to simplify the presentation as much as possible and will not overload it with cumbersome formulas. So that there is simply a general understanding of the issue.

Light flow

Light, as is known, has a wave nature. In a certain range of wavelengths, electromagnetic radiation is perceived by the human visual organs, that is, it becomes visible. The approximate boundaries of this range are from 400÷450 nm (red part of the spectrum) to 630÷650 (violet region).

Electromagnetic waves are a carrier of energy - it is the energy of the Sun that provides life on Earth. But let's digress from astronomical categories and return to ordinary light sources.

So, since a source emits light, this means radiation and transfer of a certain energy. The amount of this radiant energy (We) transferred per unit time is called radiant flux (Fe). And it is measured in watts.

However, we are talking about lighting, that is, the perception of color by human vision. And estimating the amount of energy “by eye” means immediately introducing a large error. For example, two sources with equal radiation power, but with different glow colors, will also be perceived by the eye differently.

To unify this parameter, a special physical quantity was introduced - luminous flux (F). This is also an indicator of the power of the radiant flux, but only that part of it that is perceived by the average healthy human eye.

Luminous flux can also be measured in watts (this is rather an energy indicator), or in lumens (light indicator). In practice, lumens are usually used.

For the exact value of one lumen, radiation from the central, green part of the visible spectrum, with a length of 555 nm, was taken as a standard.

So, it is accepted that a radiant flux with a wavelength of 555 nm and a value of 1 watt corresponds to 683 lumens. Why such a strange coefficient? It’s just that the final approval of this unit in the SI system took place in 1979, and the first experiments in photometry with the introduction of the luminous flux indicator began to be carried out long before that. At that time, when electric lighting did not yet exist, and an ordinary candle served as a more or less stable, “reference” light source. And the established ratio of energy watt and light lumen was recalculated over time and passed down to the present day.

Let us remind you once again that the watts mentioned above, which can also be used to measure the luminous flux, have nothing to do with those indicated on the lamp packaging. It shows the consumption of the lamp, that is, the amount of energy that it will “take” from the network. We should be more concerned about its energetic light output - how much visible radiant energy it will “give out”. So, when choosing a lamp, it would be much more correct to pay attention not to ephemeral comparative analogies in watts, but to the clearly indicated value of the luminous flux in lumens.

Luminous output

This is a very interesting quantity in practical terms, since it essentially characterizes the efficiency of the light source. It is important to choose a lamp not based on its electrical power consumption, but on how this power is used when converted into light energy.

So, the luminous output value shows how much luminous flux is produced by the lamp when converting one watt of expended energy. It is clear that it is measured in lumens per watt (lm/W).

The conversion of one type of energy into another is carried out in different ways. For example, in conventional incandescent lamps the resistive principle is used - the glow is caused by a red-hot coil with high electrical resistance. It is clear that this is accompanied by huge heat losses. More efficient are modern lighting devices based on the principles of glow of semiconductor matrices when current is passed or specially selected gas mixtures are ionized. Here, significantly less energy is wasted on unnecessary heating.

It was already mentioned above that the peak of normal perception of light by the human eye occurs at a wavelength of 555 nm. And under ideal conditions, with complete conversion of electrical energy into a monochromatic light flux of the specified wavelength, that is, with absolutely no losses, it is theoretically possible to achieve a light output of 683 lm/W. This is called an ideal light source, which, alas, does not exist in nature.

The table below shows comparative characteristics for the most commonly used lamps in everyday life - incandescent, fluorescent and LED. It is clearly visible how more economical the use of modern light sources becomes, that is, how the luminous efficiency increases.

(The values in the table are approximate. In any category of lamps there may be deviations in one direction or another - this depends on the quality of the particular model. But the table presents the general picture quite clearly).

Luminous flux, Lm	Incandescent lamps		Fluorescent lamps		LED bulbs
Power consumption, W	Light output, lm/W	Power consumption, W	Light output, lm/W	Power consumption, W	Light output, lm/W
250	20	12.5	5÷7	41.7	2÷3	100
400	40	10	10÷13	36.4	4÷5	88.9
700	60	11.7	15÷16	45.2	6÷10	87.5
900	75	12	18÷20	47.4	10÷12	81.8
1200	100	12	25÷30	43.6	12÷15	88.9
1800	150	12	40÷50	40	18÷20	94.7
2500	200	12.5	60÷80	38.5	25÷30	90.9

The specific luminous efficiency value is not always, but is still indicated by some lamp manufacturers on their packaging. This may be the inscription “light output” or “Lighting effect”. If not, then it’s easy to determine it yourself by dividing the nameplate luminous flux by the specified power consumption.

It is quite obvious that of all the lamps used in domestic conditions, LED devices have the best light output indicators - for them this indicator reaches 100 lm/W, and may even be slightly higher. But progress does not stand still, and the developers announce the imminent mass production of lamps with a light output of about 200 lm/W. But the ideal source is still oh so far away...

By the way, scientists were able to estimate the luminous efficiency of the Sun, and it is not so high: approximately 93 lm/W.

The luminous output of various types of light sources is also described in the proposed video:

Video: What is luminous efficiency, and what is the practical application of this parameter?

The power of light

In physics there is the concept of a point source of light - it propagates radiation exactly the same in all directions. In practice, if this happens, it is extremely rare, and even then - with some simplification of concepts. In fact, the light flux in different directions is uneven. And in order to estimate, let’s say, its spatial density, they operate with the magnitude of the light intensity. And to understand what it is, you will also have to remember the concept of a solid angle.

Let's start with geometry. So, a solid angle is a part of space that unites all rays emanating from one point and intersecting a certain surface (it is called a subtending surface). In photometry, of course, this is an illuminated surface. This angle is measured in special quantities - steradians (sr), and is usually denoted in formulas by the symbol Ω .

The magnitude of the solid angle is the ratio of the area of the subtending surface to the radius of the sphere.

Ω = S/R²

That is, if we take, for example, a sphere with a radius of one meter, then a solid angle of one steradian will “cut” a spot on its surface with an area of one square meter.

Why know this? The fact is that the concept of luminous intensity is directly related to the solid angle. Specifically, a luminous flux of one lumen, propagating in a space limited by a solid angle of one steradian, has a luminous intensity of one candela. Mathematically, this relationship looks like this:

I = Ф/ Ω

And if we talk about the energy intensity of light equal to one candela, then this is 1/683 W/sr.

By the way, the candela is one of the seven basic quantities of the SI system.

Candela literally means candle in Latin. This is exactly that “relic of the past” that was already mentioned above, but it very clearly shows the entire interconnection of quantities.

Let's explain in the figure:

So, there is a point source of light - a candle. Its burning wick emits light with an intensity of one candela (item 1).

In a space limited by a solid angle equal to one steradian (item 2), a luminous flux (item 3) equal to one lumen will propagate. At a certain distance from the source (radius of the sphere - position 4), this flow illuminates the surface of a certain area (position 5). Looking ahead, we will immediately say that if the area is equal to one square meter, then under such conditions in this “light spot” an illumination equal to one lux (lx) is provided.

If we return to the candle as a reference light source, then it is easy to calculate its total luminous flux. A complete sphere has a solid angle of 4π, that is, with slight rounding, it is equal to 12.56 steradians. This means that a candle emitting light of one candela in all directions produces a total luminous flux of 12.56 lumens.

It is interesting that not so long ago the emissivity of light sources was assessed “in candles”. For example, they said that you need a “light bulb for sixty candles.” Sellers and buyers understood each other perfectly - a 60 W incandescent light bulb was purchased, although, in fact, these quantities are in no way related to each other in this case, from the point of view of physics. And what’s funny is that it was close to the truth.

Let's see - 60 candles of 12.56 lumens will give a total of 753.6 lumens. Let's look at the table above - an incandescent lamp with a consumption of 60 watts has a luminous flux of approximately 700 lumens. Very close!

But, we repeat, a correct assessment of light sources should still be carried out in lumens.

Light brightness

Another parameter worth considering is the brightness of the light source. The fact is that there is practically no need to deal with point sources. That is, most sources have some specific emitting surface. And with an equal luminous flux, but a different area of light emission, it will be perceived differently by vision.

That is, in essence, brightness is the strength of light emitted from a certain unit area of the visible surface of a light source.

L = I/S

It is clear that the unit of brightness will be candela per square meter.

This is an important value, since the organs of vision, when looking at a light source, react, rather, not to the intensity of light as such, but rather to brightness. When its value is large (over 160 thousand candelas per square meter), the light can cause eye irritation, pain, and tearfulness. That's why lighting manufacturers produce lamps with frosted bulbs. With virtually no loss of luminous flux, the radiation does not come specifically from an incandescent filament or LED with their small areas, but from a much larger surface area of the bulb. This glow is much safer for the retina of the eye and is perceived much more comfortably by vision.

Surface illumination

Finally, we got to the lighting. This value can be considered the most applied, since it is the illumination of a particular area that evaluates the overall operation of lighting devices.

Figuratively speaking, illumination (E) is the surface density of the luminous flux (F) distributed over a particular area (S). If we approach it with some simplification, then this can be expressed by the following formula:

E = Ф/ S

As we saw above, one lumen of luminous flux on an area of one square meter creates an illumination equal to one lux (lx).

Illumination depends on a number of factors, even if you do not take into account the own characteristics of the light source.

Firstly, the further the source is located from the illuminated surface, the larger the area of the “light spot” (remember the solid angle cone). That is, the luminous flux is distributed over a larger area. Moreover, as we remember, this dependence is quadratic. That is, when the distance changes by half, the illumination will decrease by four times, by three times by nine times, etc.

If we consider a point source, we can apply Kepler’s formula:

E = I / r²

We will not repeat the meaning of the quantities included in the formula - they are given above.

Secondly, the Kepler formula shown above is valid only for a surface perpendicular to the direction of the light flux. In reality, of course, this does not happen often. That is, in the case when the illuminated plane is located at some angle α to the direction of the flow, corrections have to be made for this:

E = (I / r²) × cos α.

Remember - when you need to illuminate a surface as brightly as possible, you point the flashlight perpendicular to it. But if you place it at an angle, the illumination will drop sharply, since the light seems to be “smeared” across the surface.

Thirdly, the illumination of a particular area also depends on its, so to speak, surroundings. The fact is that most surfaces do not absorb all the light that hits them, but largely reflect it. And thus they themselves become original sources of light.

Let's remember what was said in the section about the brightness of the glow. Yes, indeed, the brightness of such illuminated areas is not particularly high. But the radiation comes from a decent area, and as a result a very significant luminous flux is created.

And the brightness of such an illuminated surface depends both on its illumination and on its diffuse reflectivity, which has a separate name - albedo. The higher the albedo, the brighter the glow. And since it’s brighter, the “secondary” color flow is more studied.

Some visual examples of reflected light. A sheet of white paper with illumination of only 50 lux will have a brightness of 15 cd/m². The glow of the full moon (and this, as we know, is sunlight reflected from its surface) is characterized by a brightness of 2500 cd/m². And the surface of pure white snow on a sunny day reaches a brightness of up to 3000 cd/m². Quite a lot!

This phenomenon is very widely used in the organization of lighting and in the design of rooms. Entire model lines of lamps are produced that are specially designed to be directed towards walls or ceilings, that is, it is the illuminated areas that are included in the work of general lighting of the room. The same effect is used when creating multi-tiered ceiling structures with LED strip lighting.

It is easy to guess that the illumination of the room will depend on the chosen style of its decoration. The same light bulb, say, in a white room will provide much greater illumination than in one painted in dark colors.

Since the final expected result of the operation of lighting devices is the creation of comfortable and healthy lighting indicators in the room, it is the value of surface illumination that is subject to regulation. Legislative acts (SNiP and SanPiN) indicate what illumination should be achieved in various rooms, depending on their purpose.

Thus, the current SNiP 23-05-95 in its updated version (Code of Rules SP 52.13330.2011) specifies the following standard illumination indicators for residential buildings:

Type (purpose) of the premises

Illumination standards in accordance with current SNiP, lux

Type (purpose) of the premises	Illumination standards in accordance with current SNiP, lux
Living rooms	150
Children's rooms	200
Office, workshop or library	300
Cabinet for precision drawing work	500
Kitchen	150
Shower room, separate or combined bathroom, bathroom	50
Sauna, locker room, swimming pool	100
Entrance hall, corridor, hall	50
Entrance lobby	30
Stairs and landings	20
Wardrobe	75
Sports (gym) room	150
Billiard room	300
Storage room for strollers or bicycles	30
Technical rooms – boiler room, pump room, electrical control room, etc.	20
Auxiliary passages, including in attics and basements	20
Area at the main entrance to the house (porch)	6
Area at the emergency or technical entrance	4
Pedestrian path at the entrance to the house for 4 meters	4

In this case, the assessment of illumination should be carried out on a horizontal plane at floor height. For stairs - both at floor height and on transition platforms and steps.

To assess the level of illumination, special devices are used - lux meters. They consist of a photodetector with a spherical sensor surface, and a converter unit with an analog (arrow) or digital indication of readings.

It is clear that a lux meter is a highly specialized, expensive device that is used by specialists, and which is absolutely not required to have at home. But understanding the basic photometric quantities will not hurt any owner of a house or apartment.

For what? - many may ask. Yes, at least in order to be able to independently plan the use of certain light sources in order to achieve the required illumination. After all, the health and general mood of all family members directly depends on it.

The practical position of this knowledge will be discussed in the next section of the publication.

Colorful temperature

To finish the conversation about the main characteristics of light sources, it is necessary to dwell on their color temperature.

With completely equal indicators of the emitted luminous flux, one light bulb can give a warm yellowish color, another - a neutral white, and a third, for example, can glow with a cold shade of blue. How to distinguish them by this parameter? A special color temperature scale has been developed for this purpose.

Let's make a reservation right away - there is no connection between the air temperature in the room or the heating temperature of the light source itself. The glow of a physical body heated to high temperatures is simply taken as a standard.

Any body, if its temperature is above absolute zero, is itself a source of infrared radiation. As the temperature rises, the wavelength of this radiation changes, and at a certain moment it reaches the visible part of the spectrum.

Probably everyone has observed this - when heated, a metal rod first turns red, then begins to glow with a bright red light; you can heat it, as they say, “white-hot.” And when performing electric welding work, when the arc temperature reaches very high levels, the melting metal can acquire a blue tint.

It is this gradation that forms the basis of the color temperature scale. It is indicated in Kelvin - and on the scale you can see what kind of glow the lamp will emit.

This color temperature is usually indicated in the lamp labeling. Sometimes it is accompanied by a text explanation, or even a miniature scale showing in which region of the visible spectrum the lamp will glow.

The choice of lamps based on their color temperature depends on what kind of environment you plan to maintain in the room. Of course, a subjective factor will also play a significant role here - that is, the preferences of the owners. And there are no ready-made “recipes” for this. But the table below provides a recommended overview of lamps based on their glow. Perhaps this will help someone when choosing.

Colorful temperature

Visual perception

Possible definitions of the created atmosphere

Typical Applications

Colorful temperature	Visual perception	Possible definitions of the created atmosphere	Typical Applications
2700 K	Warm light	Open, warm, friendly, cozy, relaxing	Living rooms, hotel lobbies, small boutiques, restaurants, cafes
3000 K	White light	Intimate, friendly, conducive to communication	Living rooms, libraries, shops, offices
3700 K	Neutral light	Friendly, conducive to communication, giving a feeling of security, increasing attentiveness	Museums and exhibition halls, bookstores, offices
4100 K	Cold light	Focus-promoting, clean, clear, productive	Training premises, design bureaus, offices, Bolgitsy, large stores, train stations
5000 - 6500 K	Cold daylight	Disturbing, overly bright, emphasizing colors, sterile, tiring over time	Museums, jewelry stores, some offices in medical institutions

Lighting parameters

Electric lamps of various designs can be used as a light source; as an alternative, LED lighting has recently begun to be used more and more often, where the light source is semiconductor elements - LEDs.

Parameters of practical interest for choosing a particular lighting device or light source are listed here and will be discussed.

This is the power of light (optical) radiation, measured in lumens (lm). Omitting theoretical calculations and definitions, I will say on a purely everyday level - this is the amount of light emitted by the source, the larger it is, the brighter the light. What has been said is very abstract, so far we cannot derive any benefit from it, so let’s move on.

Determines the ability of a light source to convert electrical energy into light, measured lumen/watt (lm/W), which is essentially an efficiency factor.

An ideal source is capable of delivering 683 lm/W; in practice, this value is naturally less. For incandescent lamps, for example, the luminous efficiency is 10-15, fluorescent lamps up to 75, and high-power LEDs more than 100 lm/W.

Since everyone is well aware of a 100 W incandescent lamp, they can now imagine the luminous flux of 1200 lm that it emits. In addition, this indicator allows you to evaluate the level of energy savings. Obviously, with the same light output, a fluorescent lamp consumes 4-5 times less electrical energy than an incandescent lamp.

This parameter characterizes the amount of luminous flux per unit area. It is measured in lux (lx). 1lx=1lm/1sq.m. Illumination depends on the design of the reflector, the distance to the light source, and their number.

To estimate, the normal illumination for reading is 500 lux. Illumination on a sunny summer day at the latitude of Moscow can reach 100,000 lux, and on a full moon - up to 0.5 lux.

Radiation of a certain color is characterized by its wavelength. Visible radiation of red color has the shortest wavelength, blue - the longest. To simplify as much as possible, color temperature characterizes the color of radiation. It's very primitive, but it's enough for us.

It is an indicator of the naturalness of perceived colors. The higher the value of this index the lighting device (light source), the better the color rendition. A color rendering index of 70-100 characterizes color rendering from good (70) to excellent (90-100).

The materials presented on the site are for informational purposes only and cannot be used as guidelines or regulatory documents.

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Technical characteristics of fluorescent lamps - what you need to know when choosing In most cases, the rounded value of 683 lm W is used with an accuracy sufficient for any practical application. Ask, I'm in touch!