| English | Light-emitting diode (LED) |
|---|---|
| Bahasa Melayu | Diod pemancar cahaya (LED) |
| 中文 | 发光二极管（LED） |
Definition
A semiconductor diode that emits light when a current flows through it in the forward direction.
In exam terms
A light-emitting diode (LED) is a semiconductor diode that gives out light when current flows through it in the forward direction. Like any diode it conducts one way only, but its energy of recombination is released as light rather than mostly heat.
It has no SI unit of its own; the current through it is measured in amperes (A) and the voltage across it in volts (V).
A correct exam sentence: "The LED lights up only when the p-terminal is connected to the positive terminal of the supply so it is forward biased." An LED must always be protected by a series resistor to limit the current, or the large forward current will damage it.
Do not confuse it with…
Do not confuse an LED with an ordinary rectifying diode. Both allow current in one direction only, but a rectifier is used to convert a.c. to d.c. and does not emit useful light, while an LED is designed to emit light and is often used as an indicator.
Also distinguish forward bias from reverse bias: in reverse bias the LED does not light and carries almost no current.
In Paper 2 you may be asked to state the function of the series resistor, explain why the LED lights only in forward bias, or draw the correct circuit symbol with the arrow marking current direction.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)