Efficiency
This is an oversimplification, but it gives the basic idea. Every energy transfer loses energy. The percentage of energy that does what you want is something worth looking at. The controversy of switching light bulbs seems to have passed, but when Republican President Bush and the Democratic Congress in the mid 2000s were looking at ways to decrease the US dependence on outside energy sources, phasing devices that wasted 90% of the energy put in seemed like a good place to start. There was an outrage over this, partly because the transition technology of compact fluorescent bulbs wasn't great, but with the advent of LED bulbs it seems that most are thrilled for the switch and the 75% reduction in energy use.
Internal combustion engines like we have in cars are also very inefficient, but there are physical laws that prevent them from getting much better (see Carnot's law.) Fuel economy has been increased enormously in recent years, however, because there's many other things that can be tweaked to increase efficiency (lightening weight, improving aerodynamics, etc)
Efficiency
This is an oversimplification, but it gives the basic idea. Every energy transfer loses energy. The percentage of energy that does what you want is something worth looking at. The controversy of switching light bulbs seems to have passed, but when Republican President Bush and the Democratic Congress in the mid 2000s were looking at ways to decrease the US dependence on outside energy sources, phasing devices that wasted 90% of the energy put in seemed like a good place to start. There was an outrage over this, partly because the transition technology of compact fluorescent bulbs wasn't great, but with the advent of LED bulbs it seems that most are thrilled for the switch and the 75% reduction in energy use.
Internal combustion engines like we have in cars are also very inefficient, but there are physical laws that prevent them from getting much better (see Carnot's law.) Fuel economy has been increased enormously in recent years, however, because there's many other things that can be tweaked to increase efficiency (lightening weight, improving aerodynamics, etc)