MATERIALS SCIENCE
THAN WHITE
E
dison’s classic light bulb, patented 140 years ago, famously produces 50 times more heat than light. Which
is why, after a century-long success story, it is now on the way out. Energy-saving compact fluorescent lamps (CFLs), which became available in the 1980s, have improved efficiency by a factor of five, but create their own environmental hazards due to the use of mercury vapour in their fluorescent tubes. We may be luckier with the third-
time invention of the light bulb, in the shape of LED lights, which, after a long journey through chemistry and physics, are now approaching a state close to perfection.
Blue lights
The use of light-emitting diodes (LEDs) in general lighting only became possible after the invention of blue LEDs, a quarter of a century ago, completed the colour mixing scheme. Shuji Nakamura, of Nichia Chemicals at Tokushima, Japan, produced the first high performance blue LED in 1994, based on InGaN materials. He received the Nobel Prize in physics in 2014, together with Isamu Akasaki and Hiroshi Amano who, in separate work at the University of Nagoya, had made important discoveries concerning the mechanisms required for producing GaN semiconductors for use in blue LEDs.
Complementing the LEDs available
for the red end of the visible spectrum, blue LEDs made it possible to produce white light by combining LEDs of different colours. White light LEDs made in this way are even more energy efficient than CFLs, using less than 10% of the electricity that an incandescent bulb with the same light output would need. However, having to combine
LEDs of different colours has some drawbacks in practice. Green and orange emitting LEDs are less efficient than red and blue ones, and they may change in different ways in response to environmental conditions and to equipment ageing. Therefore, researchers started to
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