The ratio of lumens emitted by a light fixture to the lumens emitted by the lamp(s) installed in that fixture. A luminaire with 0.8 efficiency is considered high whereas an efficiency of 0.6 is considered standard.

The ratio of the light emitted by the luminaire compared to the light emitted by the enclosed lamps. Luminance: At a point and in a given direction, the luminous intensity in the given direction produced by an element of the surface surrounding the point divided by the area of the projection of the element on a plane perpendicular to the given dire [..]

The ratio, expressed as a percentage, of the light output of a luminaire to the light output of the luminaire's lamp(s). Luminaire efficiency accounts for the optical and thermal effects that occur within the luminaire under standard test conditions.

The ratio of total lumen output of a luminaire to the lumen output of the lamps, expressed as a percentage.