A Light-Emitting Diode (LED) is a particular type of diode that converts electrical energy into light energy. An LED emits visible light when an electric current passes through it. LEDs are very efficient in operation, consume less power, and have a very long life. They are generally used in applications such as indicator lights, LCDs, remote controls, and many such electronic devices.
The following figure shows an LED and an internal circuit as well:
Since an LED is a diode, it allows current to flow only in one direction and, if the opposite polarity is applied it won't break—it just won't work. The positive side is called the anode (+) and the negative side is called the cathode (-). The current always flows from positive to negative. In an LED, the anode side lead/leg is always longer and is a good way to identify the anode and cathode...