LED is a kind of semiconductor that emits light when you give it some voltage. Its light production method is almost fluorescent lamp and gas discharge lamp. LED does not have a filament, and its light is not generated by the heating of the filament, that is, it does not generate light by allowing the current to flow through the two terminals. LED emits electromagnetic waves (a very high frequency of vibration), when these waves reach above 380nm and below 780nm, the wavelength in the middle is visible light, a visible light that can be seen by human eyes.

Light-emitting diodes can also be divided into ordinary monochrome light-emitting diodes, high-brightness light-emitting diodes, ultra-high brightness light-emitting diodes, color-changing light-emitting diodes, flashing light-emitting diodes, voltage-controlled light-emitting diodes, infrared light-emitting diodes and negative resistance light-emitting diodes.

application:

1. AC power indicator

As long as the circuit is connected to the 220V/50Hz AC power supply line, the LED will be lit, indicating that the power is on. The resistance value of the current limiting resistor R is 220V/IF.

2. AC switch indicator light

Use LED as a circuit for incandescent light switch indicator lights. When the switch is disconnected and the light bulb goes out, the current forms a loop through R, LED and light bulb EL, and the LED lights up, which is convenient for people to find the switch in the dark. At this time, the current in the loop is very small, and the light bulb will not light up. When the switch is turned on, the bulb is turned on and the LED is turned off.

3. AC power socket indicator light

A circuit that uses a two-color (common cathode) LED as an indicator light for an AC outlet. The power supply to the socket is controlled by switch S. When the red LED is on, the socket has no power; when the green LED is on, the socket has power.