LED is called led for short. It is made of gallium (GA), arsenic (as), phosphorus (P), nitrogen (n), etc. When electrons and holes are combined, they can emit visible light, so they can be used to make light-emitting diodes. It can be used as indicator light in circuit and instrument, or form text or digital display. Gallium arsenide diode emits red light, gallium phosphide diode emits green light, silicon carbide diode emits yellow light, and gallium nitride diode emits blue light. Due to its chemical properties, it can be divided into organic light-emitting diode (OLED) and inorganic light-emitting diode (OLED).