ITRI's AC LED Technology is New Ray in Energy-saving Lighting
2009/01/13 | By Ken LiuThe government-backed Industrial Technology Research Institute (ITRI) recently introduced two innovative light-emitting diode (LED) technologies-AC LED and LED healthcare lighting, which are both patented and will help Taiwan hone the competitive edge of its LED industry via generating royalty income.
Semiconductor devices, due to inherent characteristics, as computer chips and LEDs have been designed to work at low current ever since day one, but call for direct-current (DC) transformers to be powered by household AC (alternating current).
"However, transformer circuitry, as any other, has resistance and hence impedes around 30% of current flow, compromising electrical efficiency. So, the ideal design is to raise LED's current tolerance, allowing the removal of the transformer so LEDs can be directly powered by household AC power," says James Chu, director of Opto-Electronics Device and System Application Division (ODSAD) who leads the AC LED project.
The ODSAD came up with the idea of etching a number of "micro-LEDs" on an LED chip, which are then connected in series via "bridge" circuits. "A single LED chip can only accept low voltage, but a series of LED devices on one chip can then handle high voltage. So etch more such devices on one chip to raise the LED's voltage rating," Chu explains.
The two-way "bridge" carries AC current between anode and cathode terminals. "Before raising the voltage capacity to household levels, the anode-to-cathode current is hazardous to LEDs than the flow vice versa, but installing rectifiers can direct current to go from negative to positive. After raising current capacity and removing DC transformer, AC current is accommodated naturally," Chu explains.
He stresses that changing DC to AC makes LEDs more energy-efficient. "In addition, the technology simplifies LED lighting, hence cuts cost, by eliminating transformers, which add to cost," he notes.
The inevitable question is why, given AC LED has obvious merits, did the LED originators not build such lights powered by alternating current? "First and foremost, low-voltage technology is mature and cost efficient. Furthermore, powering low-voltage chip with high-voltage is very complicated," the director stresses. "Micro devices are not etched on DC chips, but just the reverse on AC chips. Naturally yield rates on micro devices are much harder to control than DC chips," he says. His organization is the world's first to overcome such complexity by using computer-chip process on LED chip.
70-patent Protection
Chu notes that powering LEDs with AC is ground-breaking for such lighting, enticing LED manufacturers only a year ago when technological breakthroughs were made. "For a long time, manufacturers have stayed away from AC for its prohibitive development costs due to technological complexity. But our breakthroughs have literally lit the light at the end of the tunnel for AC LED proponents," he explains. So far, ITRI's AC LED technology has at least 70 patents covering structure, chip, packaging and application.
The ODSAD has developed chips rated from one to five watts in power output. "We have achieved 50 lumens per watt with the chips, enabling a five-watt emitter to shine at 250 lumens. You'd need 30-45 watt incandescent bulbs to give off such brightness," Chu says. The organization aims to boost the performance to 80 lumen-watt after two years.
A field test, Chu has found, shows the AC LEDs becoming brighter after 2,000 hours of continual operation, suggesting a need for further studies to identify such characteristic. But AC LED has excellent lifespan compared with DC LED, Chou stresses.
To show its practicality, the ODSAD has introduced a desk lamp equipped with AC LEDs. Plus four enterprises in Taiwan have been licensed to make the LED, including chipmaker Epistar Inc. and consumer-electronics manufacturer Forward Electronics Co., Ltd., a Tatung Group affiliate that is ready to mass-produce AC LEDs.
Having begun developing the AC LED technology some four years ago, the ODSAD will not only keep improving the technology, but also, Chu notes, "plan to set AC LED application standards, which show makers the characteristics of the LED to facilitate its manufacturing."
To help Taiwan's LED industry quickly apply AC LEDs, the ITRI has helped organize over 20 local manufacturers, including Epistar, Lite-On Technology Corp., Forward and Tyntek Corp., to form a strategic alliance. Johnsee Lee, ITRI president, pointed out at the inauguration that forming such alliance would "help Taiwan's LED industry move up along the value chain to create high-value products and advantages." Although Taiwan leads the world in volume of LED supplied, he notes, it still lags behind Japan by miles in output value mostly due to low margin.
Winner of Invention Oscar
Solidly confirming its world-caliber innovation, the AC LED has won the R&D 100 Awards given by the renowned R&D Magazine of the United States. Founded in 1963, the magazine honors, recognizes innovative products yearly with its "The Oscars of Invention."
More than another feather in one's cap, winning the R&D 100 Award puts ITRI in the same league as cutting-edge product breeders as Freescale, Argonne National Laboratory, Oak Ridge National Laboratory, Los Alamos National Laboratory and NASA, all of whom are also recipients.
Equally Brilliant
ITRI's triple-patented LED healthcare or medical lighting technology is almost as brilliant as its AC LED. The lighting is valuable for good color rendering, low shadow, low temperature and luminosity, making it ideal for surgery, according to Chu.
"This medical lighting lessens shadow to only 45% to 60% at one meter than traditional lights, allowing doctors to see wounds more clearly. Also, such light is cool-emitting no infra red-that minimizes heat-related problems during surgery. Good or natural color rendering allows doctors to better identify, examine pathogens," Chu says.
One downside is that the private sector still cannot independently bridge the technological gap when developing the light, notes Chu, hence relying totally on the ITRI. The light, Chu says, gives off 9,000 lumens. The ITRI has introduced a dentist's light based on the surgical counterpart, Chu says, that is 20% more power efficient than traditional types.
A local medical-equipment manufacturer has benefited from ITRI's technology transfer and is applying for Food and Drug Administration's certification in preparation for export to the United States.
Chu figures the leading-edge healthcare LED lighting technology to help LED manufacturers in Taiwan to tap the special-purpose lighting segment, which is around 20% of the US$90 billion lighting market.