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21 Sep 2007
The city of sin sees leading chipmakers go on the offensive with claims of class-leading devices, while Seoul Semiconductor announces the first single-emitter LED to deliver 420 lm.
Chip makers Nichia, Lumileds, Cree, Seoul Semiconductor and SemiLEDs all expounded the virtues of their latest GaN LED technology at the 7th International Conference on Nitride Semiconductors, being held this week in Las Vegas.
Nichia's Yukio Narakawa kicked-off the day by announcing the development of a 1 mm x 1 mm white LED delivering 169 lm/W efficacy at 20 mA. This beats the 161 lm/W figure that Nichia reported last year, and resulted from research to improve current spreading and reduce the forward voltage.
The latest LED also offers improved performance at high drive currents, according to Narakawa. It produces 134 lm/W at 350 mA and a forward voltage of 3.1 V, and can deliver 361 lm at 97 lm/W when driven at 1 A.
Seoul Semiconductor CEO Chung Lee championed the Korean company's "Acriche" product line. The company says it has produced Although these devices "only" operate at 60 lm/W, they run directly from an AC source, which Lee sees as a key advantage.
Seoul Semiconductor says that it also plans to release a single-emitter LED that delivers a record-breaking light output of 420 lm by the end of the year. Researchers at the company have already demonstrated the device, which produces up to 420 lm at its maximum current rating of 600 mA and 350 lm at its average current rating. With a size comparable to that of a conventional high-power LED, the company believes that its new 8 W light source will help to accelerate the adoption of LEDs for mainstream lighting applications.
Philips Lumileds' best result at 350 mA still stands at 115 lm/W. This was the value announced earlier this year for its "droop-free" 1 mm x 1 mm chip, which features a double heterostructure design incorporating a thick InGaN region.
Frank Steranka, who was speaking on behalf of Lumileds, pointed out that by increasing the size of the chip, this LED can deliver higher efficacies. A 4 mm x 4 mm LED emitted 142 lm/W.
Cree's John Edmond said that the Durham chip maker's best result was 133 lm/W at 350 mA, the same value announced last week (see related story). This chip is also bigger than 1 mm x 1 mm, although Edmond did not disclose its exact dimensions.
Meanwhile, SemiLEDs, the Taiwanese chip maker that incorporates a metallic mirror into its emitters, revealed that it had also reached the 100 lm/W efficacy milestone at 350 mA. The higher efficacy comes from adding a several-micron-wide step to the textured surface of the LED structure.
Keeping to the DOE roadmap
Lumileds' Steranka also discussed the advances required to hit the US Department of Energy's stiff future targets, which include reaching 150 lm/W at 2 A by 2012.
According to him, to hit this particular milestone will require a hike in internal efficiency to 90%. Phosphor technology must also improve, as one fifth of the emission can be lost in conversion.
Although the 2012 target is demanding, Steranka believes that hitting this goal holds the key to LED adoption in solid-state lighting.
At present, the cost-per-lumen for incandescent and fluorescent lamps are $0.03–0.05 and $0.06, respectively. To compete, the corresponding figure for LEDs needs to drop by a factor of 20.
But increasing the drive current to 2 A and efficacy to 150 lm/W will deliver a nine-fold improvement. If the cost of making these improved LEDs can also be halved, then chip manufacturers will be in the right ballpark.
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