The electric light sources can be divided into three main groups, divided according to how they convert electrical energy into light. One group is that of the thermal radiators, this contains incandescent lamps and tungsten halogen lamps. The second group is made up of the discharge lamps; this consists of a large spectrum of light sources, e. g. all forms of fluorescent lamps, sodium vapour lamps and metal halide lamps. The third group consists of the semiconductors with the LEDs.