Lumen
From: https://en.wikipedia.org/wiki/Lumen_(unit) 





Lumen (unit)
The lumen (symbol: lm) is the unit of luminous flux, a measure of the
perceived power of visible light emitted by a source, in the International
System of Units (SI). Luminous flux differs from power (radiant flux) in
that radiant flux includes all electromagnetic waves emitted, while
luminous flux is weighted according to a model (a "luminosity function")
of the human eye's sensitivity to various wavelengths; this weighting is
standardized by the CIE and ISO.[2] One lux is one lumen per square metre.

The lumen is defined in relation to the candela as
1 lm = 1 cd·sr.

A full sphere has a solid angle of 4π steradians,[3] so a light source
that uniformly radiates one candela in all directions has a total luminous
flux of
1 cd × 4π sr = 4π cd⋅sr ≈ 12.57 lm.[4]




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 partly 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 1,000
lumens, concentrated into an area of one square metre, lights up that
square metre with an illuminance of 1,000 lux. The same 1,000 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
An LED lamp capable of producing 470 lumens. It consumes about one sixth
the electrical power of an incandescent light bulb producing the same
light.

Lamps used for lighting are commonly labelled with their light output in
lumens; in many jurisdictions, this is required by law.

A 23 W spiral compact fluorescent lamp emits about 1,400–1,600 lm.[5][6]
Many compact fluorescent lamps and other alternative light sources are
labelled as being equivalent to an incandescent bulb with a specific
power. Below is a table that shows typical luminous flux for common
incandescent bulbs and their equivalents.





Electrical power equivalents for different lamps[7][8][9]


Minimum light output (lumens)Electrical power consumption (watts)

IncandescentCompact fluorescentLED


Non-halogenHalogen

90 15 6 2–3 1–2

200 25 3–5 3

450 40 29 9–11 5–8

800 60 13–15 8–12

1,100 75 53 18–20 10–16

1,600 100 72 24–28 14–17

2,400 150 30–52 24–30[10]

3,100 200 49–75 32[11]

4,000 300 75–100 40.5[12]



The typical luminous efficacy of fluorescent lighting systems is 50–100
lumens per watt.

On 1 September 2010, European Union legislation came into force mandating
that lighting equipment must be labelled primarily in terms of luminous
flux (lm), instead of electric power (W).[13] That change is a result of
the EU's Eco-design Directive for Energy-using Products (EuP).[14] 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 lm.[15]
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.[16] 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.[17] 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 °C (77 °F). 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".[18]


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.[19]


Color light output

Brightness (white light output) measures the total amount of light
projected in lumens. The color brightness specification Color Light Output
measures red, green, and blue each on a nine-point grid, using the same
approach as that used to measure brightness.




SI photometric units




SI photometry quantities


QuantityUnitDimension [nb 1]Notes


NameSymbol[nb 2]NameSymbol

Luminous energy Qv[nb 3] lumen second lm⋅s T⋅J The lumen second
is sometimes called the talbot.

Luminous flux, luminous power Φv[nb 3] lumen (= candela steradian) lm
(= cd⋅sr) J Luminous energy per unit time

Luminous intensity Iv candela (= lumen per steradian) cd (= lm/sr) J 
Luminous flux per unit solid angle

Luminance Lv candela per square metre cd/m2 (= lm/(sr⋅m2)) L−2⋅J
Luminous flux per unit solid angle per unit projected source area. The
candela per square metre is sometimes called the nit.

Illuminance Ev lux (= lumen per square metre) lx (= lm/m2) L−2⋅J 
Luminous flux incident on a surface

Luminous exitance, luminous emittance Mv lumen per square metre lm/m2 
L−2⋅J Luminous flux emitted from a surface

Luminous exposure Hv lux second lx⋅s L−2⋅T⋅J Time-integrated
illuminance

Luminous energy density ωv lumen second per cubic metre lm⋅s/m3 L
3⋅T⋅J 

Luminous efficacy (of radiation) K lumen per watt lm/W M−1⋅L−2
T3⋅J Ratio of luminous flux to radiant flux

Luminous efficacy (of a source) η[nb 3] lumen per watt lm/W M−1⋅L
−2⋅T3⋅J Ratio of luminous flux to power consumption

Luminous efficiency, luminous coefficient V 1 Luminous efficacy
normalized by the maximum possible efficacy


See also: SI . Photometry . Radiometry





See also