Luminance is the concept for the luminous intensity (see chapter 2.2) emitted per unit of area of a surface in a specific direction. The surface can itself be light-emitting, or transmitting - like the surface of a lamp or the sun - but it can also reflect light from another source (like a road reflecting light from a streetlight and thus act as a secondary light source). Luminance can be defined as: The ratio of the luminous intensity from a surface in given direction to the apparent area of that surface. [4]

Example of equipment to measure