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Technical Insight

HB-LEDs continue progress towards solid-state lighting

High-brightness LEDs continue to penetrate automotive, displays, signage and decorative lighting markets, says Richard Dixon in the second of two reports from the recent Strategies in Light conference.
Although the market for high-brightness LEDs stalled in 2001, remaining flat at $1.2 billion, sales of these devices are set to recover this year. In fact, last year s lull in sales in no way reflects the current enthusiasm and technical innovation in the industry, with new applications for LEDs continuing to be the driving force behind the constant push for improved performance. Some of these applications are described here in the second of two reports from the Strategies in Light conference, held in San Francisco on February 7-8 (for part one, see "High-brightness LED market to grow after flat year in 2001").

Reliability hinders display makers

According to Dario Tabakovic of Stella Vista America, 2001 was not the best year for display companies. More than 100 of the LED display companies that have emerged in recent years, and four of the top ten, have gone out of business in the last two years. One reason Tabakovic gave for the glut of new LED screen manufacturers was that the cost of entry into the LED display business was not high. Tabakovic also highlighted a problem with current LED quality assurance practices that in some cases have led to reliability issues with large-area screens, which must last at least five years to justify the initial high cost of purchase and installation.

Despite binning, a practice employed by companies to collect devices of a certain wavelength and brightness into batches of known performance, many LEDs failed to reach the required quality level. Tabakovic expressed the hope that new standards addressing the needs of screen makers would be adopted.

Auto industry provides a big market

Inside an automobile LEDs are widely used to light the dash and instrumentation, indicators, switches and radio-display backlights. Aldo Kamper of Osram Opto Semiconductors revealed that Audi currently uses more than 200 LEDs in its models, and 320 in its top range A8. This includes more than 90 devices in both the dashboard and radio, 60 LEDs to illuminate climate-control indicators and 25 in switches. Osram estimates that around 90% of new European cars have LEDs in the radios and 80% have them in the dash clusters. Branding has taken place in this market, with each maker realizing the value of the statement made by the creative use of interior lighting: VW uses blue, BMW employs orange and Saab has chosen green.

On the exterior of the car, LEDs for the front headlamps are also being actively developed and are not far from becoming a commercial reality (figure 1). A big effort is being made to develop high-power chips, as well as optical designs for efficient light coupling.

According to Kamper, around 1000 lm per light cluster is needed for low-beam operation, and up to 3000 lm for high-beam operation. Osram is now developing a compact light source that achieves 500 lm per assembly, which is sufficient to allow a dual-beam cluster that is suitable for low-beam operation with side parking lights.

These applications benefit from the improvement in the company s standard chips. Last year its InGaN blue devices gained 60% in output power using the ATON chip, which is shaped to increase light extraction (see Compound Semiconductor February 2001, p7). Osram now plans to increase the output power a further 30% by flipping the device. Not surprisingly, this LED has the internal working title of NOTA.

This year new packages are also expected, including a high-power housing called the Dragon. This is expected to accommodate the heat from a high-brightness chip operating at up to 1 W. Further out, novel LED displays could also benefit the motorist.

Ron Steen, director of lighting research at Schefenacker Research USA, described some new approaches to automotive exterior lighting, including taillight clusters. Schefenacker has a diverse product portfolio that it has recently broadened with the acquisition of Global Light Industries. Global Light is a German manufacturer of LEDs covering the full visible range (see Compound Semiconductor February 2001, p11). Steen noted that the LED industry is still characterized by a lack of available packaging options, but that Global Light has some exciting injection molding technology that overcomes this drawback. Global Light uses molding to encapsulate its own chips and produce custom designs in a range of complex forms.

Schefenacker has since produced ultra-thin center high mounted stop lamps, scheduled for production next year. These fixtures are 10 mm deep instead of the typical 30 mm. Steen showed additional lighting examples developed for several recent concept cars, including light strips.

Dialight s Gary Durgin described LEDs in other areas of transportation (figure 2), including trains, planes and buses (85% of which are now fitted with rear LED brake-light clusters).

Jason Posselt discussed LumiLeds approach to encouraging LED adoption, which involves producing lighting systems and fixtures capable of retrofit, in addition to fully integrated system designs. The company is partnering with suppliers of driver electronics and power sources and is offering different radiation patterns suitable for a range of applications. These include beams with Lambertian, batwing, collimated and side-emitting patterns. The side emitter is called the Infinity and is set for introduction later this year.

LumiLeds continues to work on phosphors, and is searching for lower correlated color temperature values with improved color rendering (the target is 2700-3500 K for indoor lighting). The alternative approach to making white output using RGB color mixing is also being investigated.

Nichia describes LED roadmap

Nichia was unusually candid about its LED product roadmap, in part because it is now taking competition from companies such as Cree more seriously (see Compound Semiconductor March 2002, p66). Mineo Sei, head of sales in the company s Optoelectronics Division, said Nichia will be targeting reliability and is aiming at 30,000 hours for 50% lumen depreciation instead of the current 10,000 hours.

He also said that Nichia would be targeting the white LED backlighting market for cell phones with full-color displays. Already popular in Japan and Asia, demand for these displays will rise as cell-phone manufacturers introduce models with color screens to replace the simple green backlighting. To serve this market, the company has developed surface-mount InGaN white devices in 1.0 and 0.8 mm thick packages. These devices will also target PDAs, hand-held video cameras and digital still cameras. Nichia also revealed its plans for high-flux LEDs, and has since released 1 x 1 mm high-power chips (see Compound Semiconductor April 2002, p15).

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