Efficacy

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Efficacy

In lighting design, a measure of the luminous efficiency of a specified light source, expressed in lumens per watt. For daylighting, this is the quotient of visible light incident on a surface to the total light energy on that surface. For electric sources, this is the quotient of the total luminous flux emitted by the total lamp power input.

luminous efficacy

The ratio of the total emitted luminous flux, in lumens, to the total electric power consumption in watts.