What Is an LED?
A light-emitting diode glows when current crosses its semiconductor junction.
What an LED is
An LED, short for light-emitting diode, is a tiny semiconductor chip that gives off light when a small electric current passes through it in the correct direction. Unlike a filament bulb, nothing is heated until it glows. The light is produced inside solid material, which is why LEDs are small, tough and efficient.
What is inside a typical 5 mm LED
- The chip (die): a speck of semiconductor, often smaller than a grain of salt, where the light is made.
- The reflector cup: a small metal cup under the chip that directs light upwards.
- Leads and bond wire: two metal legs carry current, and a hair-thin wire joins the chip to one of them.
- The lens: a moulded plastic dome that protects the parts and shapes the beam. It may be clear or tinted.
Why people use LEDs
LEDs switch on instantly, work from low voltages, last for tens of thousands of hours and waste far less energy as heat than older lamps. They come in many colours without needing coloured filters, and they survive knocks and vibration that would break a glass bulb.
Two rules to learn first
First, an LED is polarised, so it only lights when connected the right way round. Second, an LED does not limit its own current. Connect it straight to a battery and the current can rise until the chip is damaged, so a series resistor or a current-regulating driver is always needed.
Where you will find them
Power indicators on chargers, remote controls, car lamps, torches, televisions, displays, street lights, clocks and room lighting all rely on LEDs. The same basic part appears in each of them, just built in different sizes and power levels.
Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.