It is a semiconductor diode that converts electrical energy to light energy. The light-emitting diode is composed of a PN junction as well as an ordinary diode, and also has unidirectional conductivity. When the light-emitting diode plus the positive voltage, the hole injected from the P region to the N region and the electrons injected into the P region by N, the fluorescence of the spontaneous emission is generated in a few microns in the vicinity of the PN junction with the hole in the electron and p region of N region respectively. The energy state of electrons and holes in different semiconductor materials is different. The more energy that is released when electrons and cavities are compounded, the shorter the wavelength of light emitted. Commonly used are red, green or yellow light diodes. The reverse breakdown voltage of the light-emitting diode is greater than 5 volts. Its forward volt-ampere characteristic curve is very steep, and it must be used in series to control the current of the diode. Current limiting resistor R can be computed in the following formula: = (E-UF)/IF

In the type E is the power supply voltage, the UF is the LED's positive pressure drop, if is the normal working current of the LED. The core part of the Light-emitting diode is a chip composed of P-type semiconductor and N-type semiconductor, and there is a transition layer between P-type semiconductor and N-type semiconductor, called PN Junction. In the PN junction of some semiconductor materials, the injected minority carriers, when combined with most carriers, release the excess energy in the form of light, thus converting electrical energy directly into energy. PN Junction Plus reverse voltage, a few carriers are difficult to inject, it does not glow. The diode, which is made of the injection electroluminescent principle, is called a light-emitting diode, commonly known as an LED. When it is in the positive working state (that is, at both ends plus the positive voltage), the current from the LED anode to the cathode, the semiconductor crystal emitted from the ultraviolet to the infrared color of the light, the intensity of light and current.