White LED Benchmark of 65 Lumens Per Watt Achieved
Novel chip design and the balance of multiple interrelated design parameters have enabled Cree, Inc.'s Santa Barbara Technology Center to demonstrate white LEDs with efficacies greater than 65 lumens per watt at 350 mA. The results are particularly significant because they were achieved with a pre-production prototype chip using the same package used in Cree's commercially available XLamp® 7090 high power LED, rather than a laboratory device.
This achievement is based on improved output of the primary blue emitting chip, which was combined with acommercially available yellow phosphor. The results are on par with some compact fluorescent lighting systems and up to 10 times as efficient as incandescent sources.
Cree's achievement is part of a three-year project focused on demonstrating that existing white LED technology could be successfully scaled up (in terms of electrical input/optical output power) to levels suitable for general illumination applications, with superior energy efficiency. This goal requires significant improvements in such diverse areas as chip efficiency, optical design, and thermal management.
Critical Milestone Builds on Blue LED Breakthrough
The primary light source in the white lamps is an InGaN-based blue LED that is covered with a phosphor to produce white light. Efficiency and output power of the blue chip are therefore critical parameters. Recent technical breakthroughs enabled new record performances for 1-watt class blue LEDs operating at a current of 350 mA. A key modification to Cree's experimental LED chip design resulted in a 17-20% increase in brightness and, in addition, the demonstration of packaged blue LEDs with external quantum efficiency of 40%.
Using these latest generation blue LEDs with a commercially available yellow phosphor, white LEDs were fabricated based on Cree's XLamp 7090 power LED platform, with proven long-term reliability. In spite of the blue chip's slightly higher than optimal operating voltage, the output from the XLamp devices averaged over 65 lumens per watt, with individual devices as high as 70 lumens per watt for a 0.9 x 0.9 mm2 chip operating at 350 mA. The color-coordinated temperature of the lamps was ~6000 K. Cree is targeting to make its new brighter LED chips commercially available in 2006.