SAN FRANCISCO White LEDs will replace incandescent bulbs in traffic lights and other applications, drawing less power and lasting over ten times longer, according to Shuji Nakamura, a faculty member at the University of California at Santa Barbara, in a keynote address Monday (Dec. 11) at the International Electron Devices Meeting.
Nakamura, the inventor of the blue, green and white LED and of the blue laser, had a trailblazing career as a researcher at Nichia Chemical Industries in Tokushima, Japan before recently accepted an appointment to the College of Engineering at UC Santa Barbara. In his keynote, Nakamura said that red, blue and green LEDs based on indium gallium nitride can outperform incandescent bulbs by reducing energy consumption by a factor of ten and enhancing lifetime ten to 50 times over the standard incandescent bulb, which typically lasts one year, Nakamura said.
White LEDs are twice as bright as incandescent bulbs, and will help preserve natural resources due to the use of non-toxic materials and to efficiency gains of InGaN-based LEDs, Kakamura said.
Reviewing the performance of the latest nitride-based ultraviolet blue, gree, amber and white LEDs, as well as violet/blue laser diodes, Nakamura said the development of InGaN-based compound semiconductors will open the way to solid-state semiconductor light sources. "In the past, electronic circuits were based on vacuum tubes in spite of poor reliability and durability," he said. "With the advance of solid-state semiconductor materials, all electronics are now highly reliable circuits. Only light sources are still made of an old traditional technology." Nakamura aims to change that.
At Nichia, where he began a research career in 1979, Nakamura developed a two-flow MOVCD (metal-organic chemical vapor deposition) process that "produced breakthroughs every two-to-three months" since it was developed in 1993, he said. Now the white LED, which has been described as the holy grail of semiconductor optoelectronic engineers, has Nakamura's full attention at UCSB. The MOVCD process, where gases flow in two directions instead of one, thereby improving the material quality, enabled Nakamura to make a blue LED, which led to the white LED and the blue laser.
By adding a little more indium, a blue LED can be turned into a green LED. Nakamura said he placed a novel phosphor over his blue chip to get a white light. The resultant white LED can lead to a flashlight that shines for 35 hours, up from the present six-hour limitation for an incandescent flashlight bulb, Nakamura said.
A typical 60-watt light bulb puts out a lot of electromagnetic energy in the infrared part of the spectrum which can't be seen but is felt as heat. Replacing incandescent light bulbs with white LEDs would reduce the energy needed to power lights bulbs. By eliminating the infrared radiation that produces heat from an incandescent bulb, air-conditioning costs can be reduced, he said.
Nakamura, who holds 80 Japanese patents and ten U.S. patents, said he believes material science must precede any progress in the physics of using InGaN materials. But he said he expects the material will provide a means of producing white LEDs in volume on the way to replacing incadescent light sources.
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