Just like matter, energy can be neither created nor destroyed; it can only be changed from one type to another (see Conservation of Energy). These energy changes or conversions are taking place all the time all around us, every day. When a lamp is turned on, electrical energy is changed into light and heat energy. When we eat, the chemical energy contained in our food is changed into sound energy when we speak or kinetic energy when we move something. These transfers of energy can be linked together to form energy chains. For example, it is possible to see that when we ride a bicycle we are expending, indirectly, energy from the Sun.
During all processes of energy change and transfer some energy is lost. No transfers are 100% effective, many systems and machines are very inefficient with large amounts of energy not being used for its initial purpose but being lost. For example, when you drive a car a great deal of the energy obtained from the fuel is changed not into kinetic energy, to make the car move, but into heat and sound energy. Similarly, when a lamp is lit only about 5% of the energy used is converted into light; the rest is lost as heat. A lamp, therefore, is said to have an energy efficiency of 5%. Manufacturers are constantly working to produce equipment that has a greater degree of energy efficiency, without any loss of performance.