Luminance
2-1-045
Luminance (in a given direction, at a point on the surface of a source or receptor, or at a point on the path of a beam)
The quotient of the luminous flux (d2F) leaving, arriving at, or passing through an element of surface at this point and propagated in directions defined by an elementary cone containing the given direction, by the product of the solid angle (dO) of the cone and the area (dA cos?) of the orthogonal projection of the element of surface on a plane perpendicular to the given direction.
Symbol: L
Unit: candela per square metre (cd/m2)
Reference: C.I.E. (modified)
Note 1: Brightness (G.B.) and, in French, Brillance are obsolescent terms meaning luminance. It is strongly recommended that they should not in future be used in this sense, i.e. referring to a physical quantity. In particular, Brightness should not be used in this sense, in order to avoid confusion with the use of the same word, particularly in the U.S.A., for a psychological effect (2-1-365).
Symbol: B (deprecated)
Note 2: If the luminous intensity produced by a plane luminous surface of finite area A in a particular direction (making an angle ? with the normal to the surface) may be considered uniform over all points of the surface and of value I?, then the luminance L? of the surface in the particular direction is given by
Note 3: For further explanations, see Reference: C.I.E.
Note 4: The luminance of a surface may be that of a primary light source (2-3-000) or that of a secondary light source (2-3-005).
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
