Definition
Amount of light that an object emits, in candela/m
It’s a propriety of a physical object, independent of human perception.
Not to be confused with Brightness or Lightness.
Photographic subjects
The more luminous an object is, the more it will seem bright to the human eye.
Similarly, the more it will impress the image sensor or film, leaving behind a brighter image.
Monitors
Applies to monitors. A powerful screen will be capable of high luminance.