Everyone nowdays is familiar with LEDs, they can be found in most of the current technologies. LEDs emit light with a specific voltage and current flow and are really useful because they can be used as a source of light but also as a visual feedback for the user (like on-off lights) or as a way of sending information (like the Infrared LEDs used in remote controls). Figure 1 shows a classic LED shape used especially in hobbyist electronics, it has two pins with different lenghts: the longest is the Anode and it is the positive side while the shortest is the cathode and it is the negative side. Differenly from resistors, LEDs only allow the current flow in one direction so it is important to connect these pins correctly in the circuit.

Figure 2 shows the symbol typically used in the schematics to represent a LED, in some cases it is also written which side is Anode and Cathode in order to avoid confusions and clarify the current direction.

LEDs are created in different colors (and also shapes/dimensions) and they are typically sold in bulks as can be seen in Figure 3.

The amount of current typically required by LEDs is 20mA. On the other hand, the voltage changes and the differences depend on the color of the led but also in some cases on the dimension. Figure 4 shows a table with the typical voltage ranges associated to the different colors of LEDs.

Ohm's Law

There are also LEDs that contain multiple LEDs inside, like the one shown in Figure 5: it has 4 pins, the longest one is the common anode while the other three are associated to Red/Green/Blue cathode pins. Given that a combination of RGB colors can create other colors, by varying the voltages on the RGB pins it is possible to output different colors from the LED. It is worth mentioning that the RGB LED has also a version where the common pin is the cathode and the RGB pins are anodes, this information is essential because it impacts the design of the circuit.

This is not an exaustive guide on LEDs but overall it provides details on how they are used and what is typically available to hobbyists for their electronic projects.