Luminous intensity per unit projected area in a given direction, the photometric quantity that corresponds most closely to perceived brightness. A matte surface's luminance equals its illuminance times reflectance divided by pi. Luminance governs glare, display brightness, roadway lighting and visual comfort: a white wall at 500 lux is about 130 cd/m squared, while an exposed LED chip can exceed 10 million.
Luminance of the lens is over 20,000 cd/m squared at 60 degrees, that's why people are complaining about glare in the open office.
Also heard as
- L
- photometric brightness
Do not mix it up with
- Illuminance: Illuminance is light arriving on a surface; luminance is light leaving it toward the viewer.
Related terms
Nit
An informal but widely used name for one candela per square meter, the unit of luminance.
Illuminance
The amount of light falling on a surface per unit area, measured in lux or foot-candles.
Glare
Visual discomfort or loss of visibility caused by excessive brightness or contrast in the field of view.
UGR
Unified Glare Rating: a calculated index of discomfort glare from interior luminaires, where lower numbers mean less glare.
Photopic
Describes daylight vision, when cones dominate, providing color and sharp detail at luminances above a few cd/m squared.