The emitted optical power divided by electrical input power. For the bare-device calculation in light-emitting diode efficiency, ; a complete lamp also consumes power in its driver. Luminous efficacy, measured in lumens per watt, additionally weights the spectrum by human visual sensitivity and is a different quantity.
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Wall-plug efficiency refers to the efficiency of a device in converting electrical power drawn from a wall outlet (or other power source) into useful output power, typically in the context of electronic devices and power supplies.