Encyclopedia
Brightness
Brightness: flux emitted by a unit of visible surface in a given direction within a solid angle; ratio of luminous intensity in a given direction to the area of projection of the emitting surface onto a plane perpendicular to that direction, cd/m²
Source: "GOST 26824-2010. Interstate Standard. Buildings and Structures. Methods for Measuring Brightness"
(introduced into force by Order of Rosstandart dated April 19, 2011 No. 49-st)