Taking a more practical turn, the Royal Swedish Academy of Sciences has awarded this year’s Nobel Prize in Physics to three inventors of the blue light-emitting diode.
Isamu Akasaki and Hiroshi Amano, who worked together at the University of Nagoya, and Shuji Nakamura, who worked at Nichia Chemicals in Tokushima, developed bright versions of the devices in the late 1980s and early 1990s.
“Their inventions were revolutionary,” the Nobel Foundation said in a press release. “Incandescent light bulbs lit the 20th century; the 21st century will be lit by LED lamps.”
LEDs can produce as much as 300 lumens per watt of electrical input power, the press release goes on to note, nearly 20 times as much as incandescent bulbs yield and about four times as much as that of fluorescent lamps. The greater efficiency could help conserve resources in a world where about a quarter of the energy produced goes into lighting.
In incandescent bulbs, light is almost an afterthought; the filaments are essentially just big resistors and most of the energy is released in the form of heat.
LEDs more directly convert electricity into photons. They typically contain two layers of semiconducting materials, one engineered to contain an excess of electrons and the other an excess of holes (absences of electrons that act as positive charges). To make photons, the electrons from one side and holes from the other are drawn together. They meet at a thin, active layer between the two materials, where they join and release energy in the form of photons.
Nakamura often takes the headlines in discussions of the invention of the blue LED. But, the Nobel Foundation notes, Akasaki and Amano were the first to develop the high-quality gallium nitride used to make the blue diodes, beginning in 1986 (pdf). The three lighting luminaries, all of whom are IEEE members (Akasaki is a Life Fellow), have won multiple IEEE awards including the IEEE Edison Medal and numerous IEEE Photonics Society Awards.
With the invention of these devices, engineers could now create white light by using blue light to excite a phosphor or by combining red, green, and blue devices. LEDs now light LCD screens, are slowly pushing aside incandescent and fluorescent lighting in homes and offices, and can be used to electronically control color to better mimic the diurnal cycle. The blue LED also formed the basis for a later invention – the blue semiconductor laser.
Development on the blue LED has continued steadily since its invention. One key challenge has been LED droop, a drop in efficiency when currents are raised to produce more light. Last year, a team of researchers claimed they’d found the source of the droop, but others weren't so confident. And engineering a way to circumvent it is another matter.
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