Luminous efficacy is a figure of merit for light sources. It is the ratio of luminous flux (in lumens) to power (usually measured in watts). As most commonly used, it is the ratio of luminous flux emitted from a light source to the electric power consumed by the source, and thus describes how well the source provides visible light from a given amount of electricity.

This is also referred to as luminous efficacy of a source. The term luminous efficacy can also refer to luminous efficacy of radiation (LER), which is the ratio of emitted luminous flux to radiant flux. Luminous efficacy of radiation is a characteristic of a given spectrum that describes how sensitive the human eye is to the mix of wavelengths involved.

Which sense of the term is intended must usually be inferred from the context, and is sometimes unclear. The luminous efficacy of a source is the LER of its emission spectrum times the conversion efficiency from electrical energy to electromagnetic radiation. In some other systems of units, luminous flux has the same units as radiant flux.

The luminous efficacy of radiation is then dimensionless. In this case, it is often instead called the luminous efficiency or luminous coefficient and may be expressed as a percentage. A common choice is to choose units such that the maximum possible efficacy, 683 lm/W, corresponds to an efficiency of 100%.

The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage.

Similar to 0 things you like: