Electronic Design

High-Brightness LEDs Aglow For 2003

Over the past seven years, high-brightness (HB) LEDs have made steady and substantial gains in performance. These trends should continue into 2003, with no dramatic breakthroughs expected. The best InGaN devices, which produce light in the blue-green part of the spectrum, have conversion efficiencies on the order of 10% to 25%. In the yellow-red region of the spectrum, InGaAlP is the predominant high-brightness LED material (with some AlGaAs red still present in the market), and the best devices have efficiencies of 10% to 30%. Improvements in the performance of both device classes tend to be incremental, although several companies announced some substantial improvements in 2001. Prices steadily drop by 10% to 15% each year.

The HB LEDs market has grown dramatically since 1995. In spite of market softness in 2001, due primarily to the worldwide economic slowdown, the market for HB LEDs grew at an average annual rate of 47% from 1995 to 2001, reaching $1.2 billion. The door swung open on applications that were once not addressable with conventional (low-brightness) LEDs, fueling the high growth rate. Such applications include single- and full-color outdoor signs, traffic signals, interior and exterior automotive lighting, and backlights for LCD displays (primarily in mobile phones). In the latter market, full-color displays have driven demand for an efficient white backlight. White LEDs, which appeared on the market several years ago, are produced by adding a yellow-emitting phosphor to a blue LED. In addition to display backlights, white LEDs are used in flashlights, automobile dashboards, and a variety of specialty lighting applications.

The most significant recent development in HB LEDs is the fabrication of large-area (1- by 1-mm) chips, and associated packaging. These chips dramatically increase the amount of light emitted from a single packaged device. In the case of white LEDs, these devices produce nearly 30 lumens, compared to just over 1 lumen from a 5-mm lamp. These devices are starting to be produced in volume by Lumileds Lighting with other suppliers expected to enter the market this year.

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