Luminance is the luminous intensity per unit area. It is a measure of the brightness of a point on a surface that is radiating or reflecting light 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. Luminance is also called photometric brightness.

Luminance is often used to characterise emission or reflection from flat, diffuse surfaces. It is the measure of the brightness of a color and indicates how much luminous power will be perceived by an eye looking at the surface from a particular angle of view. Luminance is an indicator of how bright the surface will appear.

Units and Measures

Luminance is the luminous intensity in a given direction of a small element of surface area divided by the orthogonal projection of this area onto a plane at right angles to the direction.

Following are the units of Luminance:

  • SI Units: candela per square metre (cd/m2).
  • Imperial Units: candela per square feet (cd/ft2).
  • Apostilb is another unit of luminance. It is equal to the luminance of a perfectly diffusing surface emitting or diffusing light at the rate of 1 lumen/m2.
  • Stilb is a unit of luminance (photometric brightness) equal to 1 candela/cm2.

Useful References

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