luminous efficacy of a source of light


NOTE: This term and its definition were changed in RP-16-17 Addendum 4. Deletions have a strike-through. New text is bold.

The quotient of the total luminous flux emitted by the total lamp power input. It is expressed in lumens per watt (lm/W).

Note: The term luminous efficiency has in the past been extensively used for this concept.

The total emitted luminous flux divided by the total source electrical input power; expressed in lumens per watt (lm/W).

Note 1: The term luminous efficacy can be applied to a single component, multiple components, or component(s) plus any associated electrical control equipment. The user will need to state the intended meaning. For example: lamp efficacy, luminaire efficacy, system efficacy (stating what the “system” is).

Note 2: Luminous efficacy as defined here is not to be confused with luminous efficacy of radiant flux.

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