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For other uses, see Luminance (disambiguation).

Luminance is a photometric measure of the density of luminous intensity in a given direction. This article deals with the usage of this term in Optics and Lighting. In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a Light source in a particular direction per unit Solid It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The solid angle, Ω, is the angle in three-dimensional space that an object Subtends at a point The SI unit for luminance is candela per square metre (cd/m2). The candela (kanˈdɛlə /-ˈdiːlə/ symbol cd) is the SI base unit of Luminous intensity; that is power emitted by a light source in a particular M^2 redirects here For other uses see M². CM2 redirects here The CGS unit of luminance is the stilb, which is equal to one candela per square centimetre or 10 kcd/m2. The centimetre-gram-second system ( CGS) is a system of physical units.

Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. Diffuse reflection is the reflection of Light from an uneven or granular surface such that an incident ray is seemingly reflected at a number of angles The luminance indicates how much luminous power will be perceived by an eye looking at the surface from a particular angle of view. In photometry, luminous flux or luminous power is the measure of the perceived power of Light. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain Luminance is thus an indicator of how bright the surface will appear. Brightness is an attribute of Visual perception in which a source appears to emit or reflect a given amount of Light. In this case, the solid angle of interest is the solid angle subtended by the eye's pupil. The pupil is the hole that is located in the center of the iris of the eye and that controls the amount of light that enters the Eye. Luminance is used in the video industry to characterize the brightness of displays. In this industry, one candela per square metre is commonly called a "nit". "Nit (unit" redirects here For the unit of information entropy see Nat (information. A typical computer display emits between 50 and 300 nits.

Luminance is invariant in geometric optics. In Mathematics and Theoretical physics, an invariant is a property of a system which remains unchanged under some transformation. 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. In photometry, illuminance is the total Luminous flux incident on a surface per unit Area. 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.

Definition

Luminance is defined by

L_v = \frac{d^2 F}{dA\,d{\Omega} \cos \theta}

where

Lv is the luminance (cd/m2),
F is the luminous flux or luminous power (lm),
\theta\, is the angle between the surface normal and the specified direction,
A is the area of the surface (m2), and
\Omega\, is the solid angle (sr). The candela (kanˈdɛlə /-ˈdiːlə/ symbol cd) is the SI base unit of Luminous intensity; that is power emitted by a light source in a particular M^2 redirects here For other uses see M². CM2 redirects here In photometry, luminous flux or luminous power is the measure of the perceived power of Light. The lumen (symbol lm) is the SI unit of Luminous flux, a measure of the perceived power of Light. In Geometry and Trigonometry, an angle (in full plane angle) is the figure formed by two rays sharing a common Endpoint, called Area is a Quantity expressing the two- Dimensional size of a defined part of a Surface, typically a region bounded by a closed Curve. M^2 redirects here For other uses see M². CM2 redirects here The solid angle, Ω, is the angle in three-dimensional space that an object Subtends at a point The steradian (symbol sr) is the SI unit of Solid angle. It is used to describe two-dimensional angular spans in three- Dimensional space

See also

External links

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SI photometry units
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; maximum possible is 683. In Photometry, luminous energy is the perceived Energy of Light. The lumen (symbol lm) is the SI unit of Luminous flux, a measure of the perceived power of Light. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units In photometry, the talbot ( T) is a nonstandard unit of Luminous energy, named in honor of the early Photographer William Fox Talbot In photometry, luminous flux or luminous power is the measure of the perceived power of Light. The lumen (symbol lm) is the SI unit of Luminous flux, a measure of the perceived power of Light. The steradian (symbol sr) is the SI unit of Solid angle. It is used to describe two-dimensional angular spans in three- Dimensional space In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a Light source in a particular direction per unit Solid The candela (kanˈdɛlə /-ˈdiːlə/ symbol cd) is the SI base unit of Luminous intensity; that is power emitted by a light source in a particular The International System of Units (SI defines seven dimensionally independent SI base units. M^2 redirects here For other uses see M². CM2 redirects here "Nit (unit" redirects here For the unit of information entropy see Nat (information. In photometry, illuminance is the total Luminous flux incident on a surface per unit Area. LUX is the principal centre for the promotion and distribution of experimental Film and Video works in the UK. In photometry, illuminance is the total Luminous flux incident on a surface per unit Area. Luminous efficacy is a property of Light sources which indicates what portion of the emitted Electromagnetic radiation is usable for human vision. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. In Radiometry, radiant flux or radiant power is the measure of the total power of Electromagnetic radiation (including Infrared, 002 lm/W
SI • Photometry
This article deals with the usage of this term in Optics and Lighting.

Dictionary

luminance

-noun

  1. the quality of being luminous
  2. the luminous flux emitted in a given direction divided by the product of the projected area of the source element perpendicular to the direction and the solid angle containing that direction, i.e. luminous intensity divided by unit area; measured in stilbs or apostilbs
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