Energy efficiency measures how much useful work is performed for each unit of energy used energy is lost as waste heat to the environment money can be saved by using less energy energy is consumed by a device as it performs work energy is conserved by energy-efficient devices

Energy efficiency measures how much useful work is performed for each unit of energy used. It is a measure of how effectively energy is used to perform a task or produce a product. The higher the energy efficiency, the less energy is wasted and the more useful work is performed with the same amount of energy.