It is a semiconductor device made of special semiconductor materials such as gallium phosphide (GaP) or gallium arsenide phosphate (CaAsP) that can directly convert electrical energy into light energy. Although light-emitting diodes are also made of PN structure like ordinary diodes, they also have unidirectional conductivity, but light-emitting diodes do not apply their unidirectional conductivity, but let it emit light for indication (display), lighting devices.