- The condition or quality of being luminous.
- Physics. The intensity of light per unit area of its source.
Dictionary:
lu·mi·nance (lū'mə-nəns) ![]() |
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| Sci-Tech Encyclopedia: Luminance |
The luminous intensity of any surface in a given direction per unit of projected area of the surface viewed from that direction. The International Commission on Illumination defines it as the quotient of the luminous intensity in the given direction of an infinitesimal element of the surface containing the point under consideration, by the orthogonally projected area of the element on a plane perpendicular to the given direction. Simply, it is the luminous intensity per unit area. Luminance is also called photometric brightness.
Since the candela is the unit of luminous intensity, the luminance, or photometric brightness, of a surface may be expressed in candelas/cm2, candelas/in.2, and so forth.
The stilb is a unit of luminance (photometric brightness) equal to 1 candela/cm2. It is often used in Europe, but the practice in America is to use the term candela/cm2 in its place.
The apostilb is another unit of luminance sometimes used in Europe. It is equal to the luminance of a perfectly diffusing surface emitting or diffusing light at the rate of 1 lumen/m2. See also Luminous intensity; Photometry.
| Computer Desktop Encyclopedia: luminance |
The amount of brightness, measured in lumens, that is given off by a pixel or area on a screen. For example, dark red and bright red would have the same chrominance, but a different luminance. Bright red and bright green could have the same luminance, but would always have a different chrominance. See luma.
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| Architecture: luminance |
The luminous intensity of any surface in a given direction per unit of projected area of the surface, as viewed from that direction; a directional property of luminous radiation.
| Wikipedia: Luminance |
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m2). A non-SI term for the same unit is the "nit". The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2.
Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance indicates how much luminous power will be perceived by an eye looking at the surface from a particular angle of view. Luminance is thus an indicator of how bright the surface will appear. In this case, the solid angle of interest is the solid angle subtended by the eye's pupil. Luminance is used in the video industry to characterize the brightness of displays. A typical computer display emits between 50 and 300 cd/m2. The sun has luminance of about 1.6×109 cd/m2 at noon.[1]
Luminance is invariant in geometric optics. This means that for an ideal optical system, the luminance at the output is the same as the input luminance. For real, passive, optical systems, the output luminance is at most equal to the input. As an example, if you form a demagnified image with a lens, the luminous power is concentrated into a smaller area, meaning that the illuminance is higher at the image. The light at the image plane, however, fills a larger solid angle so the luminance comes out to be the same assuming there is no loss at the lens. The image can never be "brighter" than the source.
Contents |
Luminance is defined by

where
is the angle between the surface normal and the specified direction,
is the solid angle (sr).| 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/m2 | 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 | ratio of luminous flux to radiant flux | |||||
| SI • Photometry | ||||||||
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