Energy efficiency is a target, to reduce the amount of energy required for products and services. For example, house insulation allows a building to use less heating and cooling energy, in order to achieve and maintain a comfortable temperature. A higher level of energy efficiency means consuming less energy while continuing to obtain the benefits to which we are accustomed (e.g. availability of lighting, heating, electric motors). Installing fluorescent lights, LED lights or natural skylights reduces the amount of energy needed to achieve the same level of illumination compared with conventional bulbs.
Increased energy efficiency results in three main benefits: higher economic efficiency, reduction of scarcity of energy resources, and reduction of greenhouse gas emissions associated with energy consumption.
The best way to understand this idea is through examples:
Energy Efficiency is when you replace a single pane window in your house with an energy-efficient one, the new window prevents heat from escaping in the winter, so you save energy by using your furnace or electric heater less while still staying comfortable. In the summer, efficient windows keep the heat out, so the air conditioner does not run as often and you save electricity.
When you replace an appliance, such as a refrigerator or clothes washer, or office equipment, such as a computer or printer, with a more energy-efficient model, the new equipment provides the same service, but uses less energy. This saves you money on your energy bill, and reduces the amount of greenhouse gases going into the atmosphere. Energy efficiency is not energy conservation.
Energy conservation is reducing or going without a service to save energy.
For example: Turning off a light is energy conservation. Replacing an incandescent lamp with a compact fluorescent lamp (which uses much less energy to produce the same amount of light) is energy efficiency.
Both efficiency and conservation can reduce greenhouse gas emissions.