1. When the forward voltage is applied to the light-emitting diode, the holes injected from the P area to the N area and the electrons injected from the N area to the P area are respectively in the vicinity of the PN junction with the electrons in the N area and the P area. The holes recombine to produce spontaneous emission fluorescence.
2. The energy states of electrons and holes in different semiconductor materials are different. When electrons and holes recombine, the energy released is somewhat different. The more energy released, the shorter the wavelength of the emitted light.
3. Commonly used are diodes that emit red, green or yellow light. 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 with a current-limiting resistor to control the current through the diode.