lumen
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(lū'mən) 
n., pl., -mens, or -mi·na (-mə-nə).
n., pl., -mens, or -mi·na (-mə-nə).
- Anatomy. The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.
- (Abbr. lm) Physics. The unit of luminous flux in the International System, equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.
- Botany. The cavity bounded by a plant cell wall.
[Latin lūmen, an opening, light.]
lumenal lu'men·al or lu'min·al adj.Related Videos:
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lumen
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Symbol lm. The SI unit of luminous flux equal to the flux emitted by a uniform point source of 1 candela in a solid angle of 1 steradian.
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[Etymology: Lat: ‘light’] luminous flux. Symbol lm. SI, Metric-m.k.s. 1948 Having been proposed as lumen in 1896 and long accepted
[Moon P. J. Opt. Soc. Amer. Vol. 32, 348-62 (1942)], then accepted into the SI in 1948 as new lumen, identically candela·steradian (cd·sr). The following are among the coherent derived units:
• lm·m-2 = lux for luminous exitance, illuminance;
• lm·W-1 for luminous efficacy;
• lm·s for quantity of light;
• lm·h for quantity of light, used, similarly to kW·h, in illumination.
The lumen is the luminous flux emitted from a point-source of uniform intensity of 1 candela into unit solid angle; the total spherical intensity of such a source is therefore 4π lm = 12.566 37~ lm. The power of such a flux depends on the wavelength of the light, 540 THz being the standard for the candela.
History
The term appears to have been introduced before 1900, and adopted officially in France in 1919, applying to the candle in its successive forms, before being adopted internationally (as new lumen) in 1946 with the ‘new candle’; see candela for the history of the candle.
| 1946 | CIPM: ‘4. New lumen (unit of luminous flux). - The new lumen is the luminous flux emitted in unit solid angle (steradian) by a uniform point source having a luminous intensity of 1 new candle.’ |
| 1948 | 9th CGPM ‘lumen’ adopted in place of new lumen.see note below |
[Le Système International d'Unités (Sèvres, France: Bureau International de Poids et Mesures, 1985)]
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A unit of measurement of the amount of brightness that comes from a light source. Lumens define "luminous flux," which is energy within the range of frequencies we perceive as light. For example, a wax candle generates 13 lumens; a 100 watt bulb generates 1,200 lumens.
Lumen Ratings for Data Projectors
When choosing a data projector, the lumen rating is an important specification. In a darkened room, 500 lumens may be ample; however, in a conference room with normal lighting, 1,000 lumens would be better. In a room with daylight, 2,000 lumens is preferred. The standard lumen rating of a data projector is the average of photometer readings at several points on a full white image on the screen. See ANSI lumen, Lm/W, candela and spectrum.
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Any cavity, such as that of a blood vessel or the alimentary canal, enclosed within a cell or tissues.
Unit Conversions:
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lumens
To convert from lumens to:
spherical candle power,
multiply by .07958.
watt,
multiply by .001496.
Related measurements:
lumens/sq. ft
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Luminal
IN BRIEF: n. - A long-acting barbiturate used as a sedative.
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- (pl. lumens) symbol: lm; the SI derived unit of luminous flux, equal to the quantity of visible electromagnetic radiation emitted per second in a cone of unit solid angle (one steradian, sr) by a uniform point source of unit luminous intensity (one candela, cd); i.e. 1 lm = 1 cd sr.
- (pl. lumina) the cavity or passageway of a tubular organ, such as a blood vessel, duct, or length of gut.
- the volume enclosed within the membranes of a mitochondrion or of the endoplasmic reticulum, or of microsomes prepared from cells.
- the space enclosed by the walls of a plant cell that no longer contains a protoplast.
- the bore of a catheter, hollow needle, or other tubular device.
| luliberin, luffin, lufenuron | |
| lumichrome, lumiflavin, lumigenic substrate |
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Pl. lumina [L.]
1. the cavity or channel within a tube or tubular organ, as a blood vessel or the intestine.
2. the SI unit of light flux.
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(lōō'mən)
n
n
The space within a tube structure, such as a blood vessel, tube, or duct.
Random House Word Menu:
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categories related to 'lumen'
- Physiology - lumen: cavity within tubular structure
- Optics - lumen: unit of luminous flux on surface, all points of which are at unit distance from a point source of one candle
Wikipedia on Answers.com:
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Lumen (unit)
The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power (radiant flux) in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux measurements indicate the total power of all light emitted, independent of the eye's ability to perceive it.
The lumen is defined in relation to the candela as
A full sphere has a solid angle of 4·π steradians,[1] so a light source that uniformly radiates one candela in all directions has a total luminous flux of 1 cd·4π sr = 4π ≈ 12.57 lumens.[2]
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Explanation
If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, the total luminous flux emitted into that angle is one lumen (1 cd·1 sr = 1 lm). Alternatively, an isotropic one-candela light-source emits a total luminous flux of exactly 4π lumens. If the source were partially covered by an ideal absorbing hemisphere, that system would radiate half as much luminous flux—only 2π lumens. The luminous intensity would still be one candela in those directions that are not obscured.
The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m2.
A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens. So a lumen represents at least 1/683 watts of visible light power, depending on the spectral distribution.
Lighting
See also: LED lamp and Incandescent light bulb
Lamps used for lighting are commonly labeled with their light output in lumens; in many jurisdictions this is required by law.
A 23 watt compact fluorescent lamp emits about 1,500–1,600 lm.[3][4]
On 1 September 2010, European Union legislation came into force mandating that lighting equipment must be labelled primarily in terms of lumens, instead of watts of electricity consumed.[5] This change is a result of the EU's Eco-design Directive for Energy-using Products (EuP).[6] For example, according to the European Union standard, an energy-efficient bulb that claims to be the equivalent of a 60 W tungsten bulb must have a minimum light output of 700-750 lumens.[7]
To estimate lumens from watts for various types of lamp, see luminous efficacy.
Projector output
ANSI lumens
The light output of projectors (including video projectors) is typically measured in lumens. A standardized procedure for testing projectors has been established by the American National Standards Institute, which involves averaging together several measurements taken at different positions.[8] For marketing purposes, the luminous flux of projectors that have been tested according to this procedure may be quoted in "ANSI lumens", to distinguish them from those tested by other methods. ANSI lumen measurements are in general more accurate than the other measurement techniques used in the projector industry.[9] This allows projectors to be more easily compared on the basis of their brightness specifications.
The method for measuring ANSI lumens is defined in the IT7.215 document which was created in 1992. First the projector is set up to display an image in a room at a temperature of 25 degrees Celsius. The brightness and contrast of the projector are adjusted so that on a full white field, it is possible to distinguish between a 5% screen area block of 95% peak white, and two identically sized 100% and 90% peak white boxes at the center of the white field. The light output is then measured on a full white field at nine specific locations around the screen and averaged. This average is then multiplied by the screen area to give the brightness of the projector in "ANSI lumens".[10]
Peak lumens
Peak lumens is a measure of light output normally used with CRT video projectors. The testing uses a test pattern typically at either 10 and 20 percent of the image area as white at the center of the screen, the rest as black. The light output is measured just in this center area. Limitations with CRT video projectors result in them producing greater brightness when just a fraction of the image content is at peak brightness. For example the Sony VPH-G70Q CRT video projector produces 1200 "peak" lumens but just 200 ANSI lumens.[11]
SI photometry units
SI photometry units
| Quantity | Symbol[nb 1] | SI unit | Symbol | Dimension | Notes | |||
|---|---|---|---|---|---|---|---|---|
| Luminous energy | Qv [nb 2] | lumen second | lm⋅s | T⋅J [nb 3] | units are sometimes called talbots | |||
| Luminous flux | Φv [nb 2] | lumen (= cd⋅sr) | lm | J | also called luminous power | |||
| Luminous intensity | Iv | candela (= lm/sr) | cd | J | an SI base unit, luminous flux per unit solid angle | |||
| Luminance | Lv | candela per square metre | cd/m2 | L−2⋅J | units are sometimes called nits | |||
| Illuminance | Ev | lux (= lm/m2) | lx | L−2⋅J | used for light incident on a surface | |||
| Luminous emittance | Mv | lux (= lm/m2) | lx | L−2⋅J | used for light emitted from a surface | |||
| Luminous exposure | Hv | lux second | lx⋅s | L−2⋅T⋅J | ||||
| Luminous energy density | ωv | lumen second per metre3 | lm⋅s⋅m−3 | L−3⋅T⋅J | ||||
| Luminous efficacy | η [nb 2] | lumen per watt | lm/W | M−1⋅L−2⋅T3⋅J | ratio of luminous flux to radiant flux | |||
| Luminous efficiency | V | 1 | also called luminous coefficient | |||||
| See also: SI · Photometry · Radiometry | ||||||||
- ^ Standards organizations recommend that photometric quantities be denoted with a suffix "v" (for "visual") to avoid confusion with radiometric or photon quantities.
- ^ a b c Alternative symbols sometimes seen: W for luminous energy, P or F for luminous flux, and ρ or K for luminous efficacy.
- ^ "J" is the recommended symbol for the dimension of luminous intensity in the International System of Units.
See also
References
- ^ "Lesson introduction to solid angles". http://www.algebra.com/algebra/homework/Bodies-in-space/Introduction-to-Solid-angles.lesson. Retrieved Oct.4, 2010.
- ^ Bryant, Robert H. "Lumens, Illuminance, Foot-candles and bright shiny beads…". The LED Light. http://www.theledlight.com/lumens.html. Retrieved Oct.4, 2010.
- ^ "Osram Dulux EL electronic energy-saving lamps" (pdf). Osram.dk. http://www.osram.dk/osram_dk/Professionelle/Brochurer_&_kataloger/Energispareprer_og_kompaktrr/e21_DULUX_EL_teknisk_guide.pdf. Retrieved Jan. 04, 2009.[dead link]
- ^ "Conventional CFLs". Energy Federation Incorporated. http://www.energyfederation.org/consumer/default.php/cPath/25_44_784. Retrieved 2008-12-23.
- ^ "Lighting now labelled in lumens". England: National Physical Laboratory. http://www.npl.co.uk/news/lighting-now-labelled-in-lumens. Retrieved March 10, 2012.
- ^ "Ecodesign for energy-using appliances". Summaries of EU legislation. the EU institutions. Feb. 2, 2010. http://europa.eu/legislation_summaries/energy/energy_efficiency/en0018_en.htm. Retrieved March 10, 2012.
- ^ "Energy-saving light bulbs: how to read the packaging". European Commission. http://ec.europa.eu/energy/lumen/overview/howtochoose/packaging/packaging_en.htm. Retrieved March 10, 2012.
- ^ "ANSI lumen article". PC Magazine Encyclopedia. http://www.pcmag.com/encyclopedia_term/0,2542,t=ANSI+lumen&i=37802,00.asp. Retrieved 2006-12-20.
- ^ "Projector Guide". CPILive.net. February 2004. Archived from the original on 3 September 2006. http://web.archive.org/web/20060903122553/http://www.cpilive.net/news_ver2_old/guides_2004/projector_guide_issue_04/office.htm. Retrieved 2006-12-20.
- ^ "ANSI method of light output measurement" (doc). 1993. http://www.hometheater1.com/tech/TB93-2.doc. Retrieved 2008-01-15.
- ^ "Sony G70 Brochure". http://www.curtpalme.com/docs/SonyG70_Brochure.pdf.
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