UK Technology Education Centre
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4: Light Emitting Diodes

Using the LED in a Fuse Tester Circuit

The bulb you used in the circuit on the previous pages can be replaced by a Light Emitting Diode (LED). This is an electronic component which glows when electricity flows through it. LEDs light like a bulb, but they only use a fraction of the power. This means that batteries will last longer if LEDs are used instead of bulbs.

LEDs must never be connected directly to a 9 volt battery or other power supply. This would damage the LED permanently because the power would be too great. In order to reduce or restrict the current going to the LED it must always be connected with a resistor in series. A resistor is an electronic component which restricts the flow of electric current.

Unlike bulbs, LEDs will only work one way round in a circuit. If you look closely at an LED, you will notice a flat part on one side. The pin or "leg" nearest the flat part is the negative and the other pin is the positive. The resistor can be connected to either the positive or negative side of the LED.

Further Reading
Circuits in Series
Circuits in Parallel

3: The Problem
5. Resistors

The Starting Point

The Pivot Point