Topic of the Moment – LEDs

Three scientists in Japan and the US have been awarded the Nobel Prize for their invention of a blue LED.

LEDs

An LED, or light-emitting diode, is a light source based on a semiconductor – materials that are neither pure conductors nor insulators but have an electrical conductivity somewhere in between.

When a voltage passes through the LED, electrons recombine with holes in the semiconductor, emitting light in the process.

The colour of the light emitted depends on the range of energies within the semiconductor where no electron states are possible – known as its “band gap”.

The first visible-light LEDs were red and, later, green, and were typically used to replace traditional light bulbs in power-indicator lights in electronic equipment such as TVs, and in simple displays such as those used by old calculators.

Creation of blue LEDs proved elusive until Shuji Nakamura of the Nichia Corporation in Tokushima, Japan, produced one 1994. The semiconductor material used in his device was indium gallium nitride, crystals of which were grown on a sapphire substrate.

The material can now be grown on silicon, reducing the cost of producing blue LEDs by up to 90%.

Blue, green and red LEDs can be combined to produce white light, so they can be used to create lamps that use vastly less electricity than incandescent bulbs.