LED, or light-emitting diode, is a light source that is more prevalent in our lives than you might know. Light is emitted when current flows through the diode and the colours are determined by the amount of energy required for electrons to cross the band gap (energy difference between the top of the valence band and bottom of the conduction band).
LEDs use far less energy, last much longer, are physically stronger even though they are smaller and switch faster than the traditional incandescent light bulbs – we still appreciate you Thomas Edison. These light bulbs are now used for aeroplanes, cars, billboards, traffic lights, medical devices, camera flashes and increasingly for general use.
The early commercial uses were for signalling and for the seven-segment number displays. This would eventually be used for common appliances such as calculators, televisions, radios, telephones and watches. LEDs were very costly at first, nearly $200 per unit, but the Monsanto Company would eventually introduce them at a lower cost and shortly after that you could pick up an LED device for less than 5c.
The LED chip is placed inside a small plastic mould which then directs the light. You might not know that this light is used to transmit data and analogue signals and not just to provide light. LEDs are used to send data over fibre optic cables, think the Internet, and to send sound to receivers that are not within listening distance of a source of the sound.
Two-way LEDs are now being explored – this means they will be able to detect and absorb light in addition to emitting light. This is done through the use of ‘Nanorods’ which allow for the contact of two semiconductor materials (diodes).