This chapter presents the types of energy sources used as a catalyst to produce light. Light can be produced through the rapid change of state of an electron from a state of relatively high energy to a ground state of lower energy. Production of artificial light can be achieved by two types of emissions. Spontaneous light emission is the most common process of light production. Stimulated light emission is another process of light production. As explained in light emission processes, energy from an external source must be supplied to a material to boost the electron from its low energy state to a higher energy state before emitting a photon. The following are the types of energy sources used to produce light: heat energy; electrical discharge; and electrical current. Another way to produce light is by applying electrical power to semiconductors, such as lasers and light emitting diodes.