What does luminance mean?
Luminance describes the brightness of a light source or surface as perceived by the eye, though in photometry it also has a precise technical meaning: the amount of luminous intensity associated with a given area. The distinction is important because two surfaces can emit the same total amount of light while differing in how bright they appear from different viewing directions. Luminance is measured in candelas per square metre, a unit also called a nit. In ordinary speech, people use it when discussing displays, lighting, photography, and the visibility of signs or images. The technical sense is especially common in physics, engineering, display technology, and the design of indoor and outdoor environments.
nounLuminance is the perceived brightness of a light or surface as determined by the amount of light reaching the eye from that direction. In photometry, it is the luminous intensity per unit area, measured in candelas per square metre, or nits.
- The quality or degree of being luminous or bright, especially as perceived by the eye.
- In photometry, the luminous intensity per unit area of a surface or source, expressed in candelas per square metre.
"The screen's high luminance made it difficult to read in direct sunlight."
"Evening light reduced the luminance of the outdoor sign."
"The photographer adjusted the monitor's luminance before comparing the images."
The plural is grammatical but uncommon; speakers usually discuss the luminance of a particular source or surface rather than referring to multiple instances.
"The technician compared the luminances of the two projection screens."
Luminance has its own unit, the nit, short for nitot: one nit equals one candela per square metre.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does luminance come from?
Luminance was formed in English in the 19th century from the Latin root meaning light, lumen, which also gives us words such as illuminate, luminous, and luminosity. The suffix -ance is used here to form a noun of quality or measurement. The related scientific vocabulary was developed in the 19th century as photometry became an important field for measuring and standardizing light.
Related word forms
How luminance is actually used
In general use, luminance means perceived brightness. In technical and scientific contexts, it has a precise photometric definition and is usually discussed alongside illuminance, contrast, and the candela.
Easily confused with luminance
Luminance refers specifically to the brightness of a surface or source as perceived in a given direction, whereas luminosity generally refers to the amount of light energy emitted by a source.