Energy efficiency

No machine turns all the energy it gets into the form we want; the rest becomes heat, sound and other forms we can't use. Efficiency is the share that comes out useful, as a percentage. A coal or gas power station turns only about a third of its fuel's energy into electricity, a filament lamp only a small part of its electricity into light, while an LED lamp gives the same light with far less. Choosing efficient machines saves fuel and money and makes less pollution.