The first light emitting diodes used in the commercial lighting world were colored. Exit signs were an early LED application. It was a perfect fit. An exit sign is a fixture that requires red or green light and one that is illuminated 24/7. The energy savings that resulted in retrofiting millions of exit signs was significant. That was back in the late 1990’s.
A decade or so later, the white LED has become common, particularly in directional lighting like spot and flood applications. With the arrival of the white LED, the opportunity for LEDs to impact general lighting energy consumption became a real possibility. However, we are not there yet.
“Cool” white can be produced at a respectable 100+ lumens per watt. “Warm” white lags behind. Philips Lumileds has “demonstrated” a warm white LED of 735 lumens at 83 lumens per watt. These are impressive numbers but still not a significant advantage over fluorescent and HID sources which can achieve higher efficacy at much lower initial cost.
Lighting constitutes about 12% of residential building energy use and 25% of commercial building energy consumption. The potential impact of LEDs in reducing lighting energy use is significant and it will eventually materialize. At the moment, LEDs are only beginning to penetrate the architectural general service lighting market. Many issues are yet to be resolved, not the least of which is the efficacy of the white LED. Below is a chart, from the U.S. Department of Energy, which shows a lumen per watt comparison of common light sources and white LEDs as well as the projection for the future.
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