White LED raises efficacy benchmark

22 Jun 2006

Researchers at Cree have demonstrated a cool-white LED that achieves an efficacy of 131 lumens per Watt at 20mA.

LED manufacturer Cree has announced LED efficacy test results of 131 lm/W for a prototype cool-white LED operating at 20 mA. The correlated color temperature was 6027 K and the results were confirmed by the US National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland.

This R&D result does not reflect the performance of current production devices, although it certainly points the way to commercial LEDs with efficacies exceeding 100 lm/W. It follows Nichia 's announcement in March that it plans to commence production of white LEDs with an efficacy of 100 lm/W in 2006.

The Cree tests were performed using prototype white LEDs fabricated using with Cree EZBright™ LED chips operating at 20 mA. EZBright chips, typically measuring 0.29x0.29 mm, are designed to be incorporated into white LEDs which are used in backlighting applications in LCD screens on mobile phones, PDAs, televisions and monitors, as well as for indoor and outdoor LED display, camera flash, gaming and indicator applications.

Cree sells EZBright chips to external customers, and does not use these chips for internal manufacture of white LEDs. Cree's high-power XLamp LED products incorporate larger chips (1x1 mm), and are designed to operate at a current of 350 mA. They consequently have lower efficacy than the smaller-chip devices.

"This is the highest level of efficacy that has been publicly reported for a white LED and raises the bar for the LED industry," said Scott Schwab, Cree's general manager for LED chips. "This result once again demonstrates Cree's leadership in LED technology and provides a glimpse into the future as to why we believe LED-based lighting products could not only save energy, but also change the way people use light."

Fritz Morgan, chief technology officer for Color Kinetics, said "Technical advancements at the component level are critical to growing the emerging white LED lighting space. Cree's results speak to the exciting developments underway that will enable new white light applications and subsequently facilitate market adoption."

Lumens-per-watt is the standard used by the lighting industry to measure the conversion of electrical energy to light. As a reference, conventional incandescent light bulbs are typically in the 10-20 lm/W range, while compact fluorescent lamps range from 50 to 60 lm/W.

• White LED manufacturers have been steadily increasing the efficacy of white LEDs in recent years. A figure of at least 70 lm/W is necessary for white LEDs to compete directly with fluorescent lights.

Previous expectations were for the milestone figure of 100 lm/W for a white LED to be reached by 2008 to 2010. However, Nichia has now adjusted its roadmap to call for a 150 lm/W device by 2007.