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, is emitted or reflected from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square metre (cd/m²).

Definition

Luminance is often used to characterize emission or reflection from flat, diffuse surfaces. The luminance indicates how much luminous power will be detected 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 billion cd/m² at noon.

Measurement

Luminance is measured with a photometer or a spectroradiometer. A photometer is designed to measure luminance in a way that is closely related to the way the human eye perceives light, while a spectroradiometer measures absolute spectral power distributions and can calculate colorimetric quantities such as luminance.

Applications

Luminance is used in many industries, including entertainment, automotive, and lighting. In the entertainment industry, luminance is used to measure the brightness of displays, such as televisions and computer monitors. In the automotive industry, luminance is used to measure the brightness of lights, such as headlights and taillights. In the lighting industry, luminance is used to measure the brightness of light sources, such as lamps and light fixtures.

See also

• Luminosity
• Luminous flux
• Luminous intensity
• Illuminance
• Radiance

References

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  Luminance
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  Etendue
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  Photometry and Radiometry Units