luminous efficacy, <of a light source>
quotient of the emitted luminous flux and the power consumed
Note 1 to entry: It has to be specified whether or not the power dissipated by auxiliary equipment such as ballasts, if any, is included in the power consumed by the light source.
Note 2 to entry: The luminous efficacy of a light source is expressed in lumen per watt (lm·W−1).
Note 3 to entry: This entry was numbered 845-01-55 in IEC 60050-845:1987.
Note 4 to entry: This entry was numbered 17-729 in CIE S 017:2011.