Energy efficiency may refer to:
- Efficient energy use, sometimes simply called energy efficiency.
- Energy efficiency in transportation.
 
- Energy conversion efficiency, the ratio between the output and input of an energy conversion machine.
- Energy conservation, efforts made to reduce energy consumption.
Famous quotes containing the words energy and/or efficiency:
“Reckoned physiologically, everything ugly weakens and afflicts man. It recalls decay, danger, impotence; he actually suffers a loss of energy in its presence. The effect of the ugly can be measured with a dynamometer. Whenever man feels in any way depressed, he senses the proximity of something ugly. His feeling of power, his will to power, his courage, his pridethey decline with the ugly, they increase with the beautiful.”
—Friedrich Nietzsche (18441900)
“Nothing comes to pass in nature, which can be set down to a flaw therein; for nature is always the same and everywhere one and the same in her efficiency and power of action; that is, natures laws and ordinances whereby all things come to pass and change from one form to another, are everywhere and always; so that there should be one and the same method of understanding the nature of all things whatsoever, namely, through natures universal laws and rules.”
—Baruch (Benedict)