Warmer whites top DOE's wish list

04 Apr 2008

The research focus on high-performance LEDs will now shift towards more warm-white LED and high-efficacy luminaire development, according to a US Department of Energy report.

DOE targets

The race between top LED manufacturers to deliver ever-increasing luminous efficacy will slow down in 2008 and 2009 as companies refocus on expanding their commercial reach. That's the finding of the US Department of Energy (DOE) 2009-2014 multi-year programme plan for solid-state lighting (SSL), which suggests that efficacy improvements will soon start to tail off.

"There are new things to deal with now that we've got the efficacy up where we'd like to see it," said Fred Welsh of Radcliffe Advisors, who helped prepare the report. "There's now more emphasis in getting warmer white light into commercial products. It's very difficult to sell cool white LEDs into some markets, particularly residential lighting."

The report is put together annually by the DOE with the help of many US-based SSL companies, including Philips' Lumileds division, Osram's US unit and Cree. Interstingly, the efficiency improvements achieved by the industry in 2007 exceeded its predictions.

In September last year, Cree delivered cold-white LED efficacy of 129 lm/W at a colour temperature of 5813 K. It also pushed up the standard for the intrinsically lower efficacy warm-white devices to 99 lm/W at a 2950 K colour temperature.

The DOE report's authors now predict that LED efficacy improvements will slow, before approaching a ceiling of 228 lm/W for cool white and 162 lm/W for warm white devices.

However, the impressive progress in 2007 has increased the overall milestones in the DOE's plan, which now call for 140 lm/W efficacy cool white and 90 lm/W warm white commercial chips by 2010. The report has also introduced a new LED goal that indicates the shift away from device efficacy: to deliver a 126 lm/W efficacy, 1000 lm output luminaire by 2012.

According to Welsh, this represents a growing feeling among the report's authors that more attention should be paid to the specific challenges of designing LED luminaires. "It's easy to ruin a good LED in a [poor] luminaire - and people are doing it," Welsh said. "We're very concerned that will sour the market."