Lumileds reduces efficacy drop-off at high currents

Chip-level technology breakthroughs at Philips Lumileds indicate that future commercial power LEDs will retain high efficacy at high drive currents of 1000 mA and above.

A well-known problem with all high-power white LEDs is that the device efficacy decreases significantly at high drive currents, especially at 1000 mA and higher. The result is that driving a power LED at 1000 mA instead of 350 mA produces a much higher light output, but at much lower efficacy.

For example, the Luxeon K2 from Philips Lumileds currently has a light output of 100 lm at 700 mA, with an efficacy of 40 lm/W. At 1500 mA, the light output is 140 lm but the efficacy is 24 lm/W.

Philips Lumileds has memorably named the problem "droop", and has announced a chip-level solution that will be implemented in commercial Luxeon LED products during 2007.

The new technology, relating to the epitaxial growth of the LED layer structures, enables efficacy values that remain high as the drive current increases. Philips Lumileds says that the new technology will enable it to deliver the industry's first high-power LEDs that deliver 70 or more lumens per watt at drive currents of 1000mA and higher.

Sampling of products incorporating the new technology is expected to begin in the next 90 days with full production in Q3 of 2007.

More light and higher efficacy for white LEDs are essential to opening new lighting markets and to expand the reach of LED lighting into residential lighting segments.

"Philips Lumileds' ability to deliver high efficacy at high currents will further enable the lighting market where maximum light output and efficacy are critical." said Frank Steranka, Executive VP Research & Development.

Clearly, while 350mA devices continue to improve in light output, they cannot deliver the light output of devices operated at 1A, 2A or even higher. Most LED manufacturers have acknowledged the need to move beyond the 350mA space and have recently announced devices that can operate at currents up to 1000mA.

"Luxeon K2 already supports a maximum current of 1.5A and with our focus on power LEDs we will continue to expand that operating range," added Steranka.

As part of the company's expansion efforts, including its new wafer fab in Singapore, Philips Lumileds is adding the necessary equipment and technology to its production lines so that the new technology can be implemented quickly.

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