LED, or
light emitting diode is as the name suggests a device which can emit
light. It has the
electrical characteristics of a
diode which means that it will pass current in one direction, but block it in the other. Standard types of LED
emit red coloured light, but other types are available that emit orange, yellow, green, or
infra-red types of light.
LEDs require typical forward operating voltage of about 2V and forward currents of 10 to 20 mA. They are widely available in sigle-LED packages, but are also available in multi-LED styles. 2-LED packages, for example, are available in either bi-colour or tri-colour forms. In the bi-colour device only one LED can be illuminated at a time, so that the device emits either a red or a green colour. IN the tri-colour device, both LEDs can be illuminated at the same time generating a yellow colour in addition to the original red and green. Multi-LED packages are also available in bargraph form, in 5 by 7 dot matrix form, and in seven segment display form.
In use, the operating current of a LED must be limited to a safe value. This can be achieved via a series resistor connected to either the anode or cathode.
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