LED diode is a special kind of diode which emits light when it is permeably polarized. Just as a regular diode, it is a polarized component which means that polarity of the voltage it is connected to is very important.

LED diode simbol

LED diode has two electrodes, anode and cathode. Anode is the positive one, while cathode is negative.

If we bring such voltage that the anode is on the more positive potential than the cathode on the LED diode, it will conduct electricity and illuminate. If the voltage is of the opposite polarity the LED will not illuminate. Besides that, nothing else will happen to it as long as the voltage is lower than that of the probe.

By permeable polarization of the LED diode, you should bear in mind the current going through the diode. The majority of the LED diodes ( except the power LEDs ) are sufficient for only a few miliampers (1mA=0.001A) to 20mA and any higher current can damage it. Therefore, the diodes in the series are always connected to a resistor which will limit the current to a desired value. The resistance value is calculated according to the following formula:

where the:

U – stands for power supply voltage
Ud – voltage on the diode at permeable polarization
Id – the current going through the diode

The data of permeable polarization (and the current through the diode) is best to be found for each and every LED diode. Characteristic values for it are 2.7-3.3 V, and 3-20 mA, where for a 5V power supply voltage we get the value of the required resistor resistance of 150-350 Ω.




As seen in the picture 2, LED diode consists of a reflecting layer that has a p-n connection which illuminates when the current flows through it. Reflecting layer, along with the p-n connection is set in the glass housing out of which anode and cathode exit.

LED diode array

If we look carefully at the LED diode, it can be seen that one pin is longer than the other. The longer pin is always anode while the shorter one is cathode. Besides, the glass rim is not round on one part, but it is straight to indicate on which side the cathode is located.

The diodes can be joined into series or a parallel, with the need to take into account that in the case of serial coupling, the voltages are added tohether while in the case of parallel connection, the currents are added together.



There are number of different LED diodes on the market, depending on their characteristics: color of light, wavelength, light intensity, angle of light, material used to make them, etc. An important characteristic is also voltage drop, and some of the listed characteristics can be found in the table below.


We hope that this tutorial provided an insight into the principle of work and basic characteristics of LED diodes. If you want to know more you can always use this tutorial. You can read more about wavelengths and types of light in this tutorial.