Energy efficiency may refer to: Energy efficiency (physics), the ratio between the useful output and input of an energy conversion process. Electrical efficiency, useful power output per electrical power consumed. Mechanical efficiency, a ratio of the measured performance to the performance of an ideal machine. Thermal efficiency, the extent to which the energy added by heat is converted to net work output or vice versa. Luminous efficiency, a measure of how well a light source produces visible light.
https://en.wikipedia.org/wiki/Energy_efficiency