Electronic Design

White Power LED Lights The Way With A 160-Lumen Output

Based on SiC wafer technology with an InGaN layer, this benchmark-setting device matches the output and efficacy levels of fluorescent lamps.

A new white-light LED sports a 160-lumen luminous flux output level at a 700-mA dc forward current and 61-lumen/W efficacy level (white color temperature of 5000 K to 10,000 K). And that's about 33% brighter than its nearest competitor, says the LED's developer, Cree Inc. The XLamp 7090 XR-E series power LED also puts out 85 lumens at 350 mA.

According to the company, the LED's 700-mA total light output is higher than other devices on the market, even at twice the current. Using a small optical source, it's 300% more uniform than previous Cree products.

Cree says that the device is as efficient as fluorescent sources, making it a cost-effective alternative for a number of general illumination and backlighting applications. Projected uses include flashlights, architecture, traffic signs, homes and offices, headlights, garage and warehouse low-bay illumination, and camera flash and projection displays.

BUILDING THE LIGHT
Based on Cree's EZBright 1000 LED chip, the XLamp 7090 XR-E is produced on a silicon-carbide (SiC) substrate that has an indium-gallium-nitride (InGaN) epitaxial layer grown on it (Fig. 1). The reflow-soldered, surface-mount chip features a small footprint of 7 by 9 mm. The maximum forward operating voltage is just 4 V, which is some 15% lower than the closest competitive product (Fig. 2).

Maximum reverse voltage is 5 V. Thermal resistance (junction to solder point) is just 8 C/W, while maximum junction temperature is 145 C. "This is the lowest thermal conductivity figure around, thanks to the use of a ceramic substrate," says Mark McClear, Cree's business director.

Lifetime for the XLamp 7090 XR-E is rated at greater than 50,000 hours or about six years (at 70% of lumen maintenance). A color version, the XLamp 7090, is available in royal blue, blue, cyan, green, amber, red-orange, and orange. The LED additionally comes in cool white, soft white, and warm white light outputs.

TECHNOLOGY BREAKTHROUGH
Thanks to a proprietary optical design, the chip delivers an optimal Lambertian radiation pattern with low emission losses and high efficiency. Other high-brightness LEDs use plastic dome lenses. But the XLamp 7090 XR-E's high-quality, floating glass dome lens provides greater light extraction.

Also, the chip is manufactured with a new phosphor deposition technique. An electrically neutral and isolated thermal path allows for the use of conventional low-cost, FR4 pc-board material in place of much costlier metal-core pc boards, which are used on other white-light LED products on the market.

Cree wasn't specific about the new LED's pricing, save to say that "it will be priced on a lumens/dollar basis, which is 20% more favorable than previous-generation Cree products and very competitive with other products on the market," explains McClear. He says the company has already shipped about a quarter of a million units.

"When talking about costs, you need to factor in maintenance and replacement costs over the lamp's lifetime," says Paul Thieken, Cree's director of marketing (see the table). "In that respect, the 7090 has a clear advantage over competitors' products."

Cree's products are already being used by Permlight Products, a developer and manufacturer of thermally managed LED lighting systems for residential and other applications. Manuel Lynch, Permlight Products' president and CEO, agrees with Cree's premise that cost-effectively replacing conventional lighting sources with solid-state high-brightness LEDs means obtaining energy savings. This can be achieved through maximizing LED efficacy ratings.

"This is a very important business metric," Lynch says. "We're now selling high-brightness light sources for under-the-counter, step, and pathway light fixtures based on the XLamps from Cree." Permlight also supplies light fixtures using Cree high-brightness LEDs for digital signage and many other applications.

Additionally, Cree recently licensed Knightbright Electronics to manufacture and sell its high-brightness white LEDs. Knightbright Electronics manufactures LED lamps, surface-mount displays, and other related LED products.

A BRIGHT FUTURE
The average selling prices of white LEDs have declined about 20% per year. Projections by the Optoelectronics Industry Development Association show that lifetime ownership costs of LED lighting systems will be less than those of incandescent lamps by next year and less than those of fluorescent lamps by 2012. Market-research firm IC Insights forecasts that high-brightness LEDs, including white LEDs used for room lighting, will account for 86% of the world's $6.7 billion total revenues for LED sales by 2010.

Solid-state lighting has become a high priority for energy-conscious government agencies worldwide, which are increasing funding for LED development. Cree has worked closely with and been funded by the U.S.

Department of Energy (DoE) under the DoE's Building Technologies Program within the Office of Energy Efficiency and Renewable Energy.

Furthermore, Cree is a charter member of the DoE's Solid State Lighting Partnership with the Next Generation Lighting Industry Alliance. The Alliance is an organization of lighting manufacturers that provides inputs to enhance the manufacturing and commercialization focus of the DoE's solid-state lighting portfolio.

Last year, the Department of Energy showed efficacy-rating projections of commercially available white LEDs reaching 150 lumens/W by 2012 and 200 lumens/W by 2020 (Fig. 3). Cree also is working with and being funded by the National Institute of Standards and Technology to develop lighting standards.

Cree Inc.
www.cree.com

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