What is luminance?
Luminance describes the brightness of a surface in a specific viewing direction. It is central to evaluating displays, luminaires and road lighting.
Definition and unit
Luminance L relates luminous intensity from an elementary surface in a direction to the projected area perpendicular to that direction. Its SI unit is the candela per square metre (cd/m²). Luminance depends on direction, so measurement geometry must be clearly defined.
How is luminance measured?
A spot meter averages luminance over its measurement field. An imaging luminance meter, or luminance camera, records a spatial map of many points at once. The luminance camera is developed by L22 for such applications; verified parameters are available in its datasheet.
Applications
Luminance measurements are used for LED displays, signs, backlit parts, architectural illumination and road lighting. Distance, focus, exposure, ambient light and calibration must match the test procedure.
Frequently asked questions
What is the unit of luminance?
Candela per square metre (cd/m²).
What instrument measures luminance?
A spot luminance meter or an imaging luminance meter, also called a luminance camera.
Is luminance the same as illuminance?
No. Luminance concerns light leaving a surface, whereas illuminance concerns light incident on a surface.