Luminous efficiency (or, more properly, efficacy), specified in lumens per watt, is a measure of the amount of visible light produced for each unit of electrical power consumed. Higher is better, and when it comes to light-emitting diodes (LEDs) of various kinds, luminous efficiency records have been made and challenged with almost dizzying frequency over the last few years.

Ken Werner
Senior Analyst and Editor

Yesterday, Nichia Corp. (Tokyo, Japan; www.nichia.com) announced the development of a white LED that produces a stunning 150 lumens per watt. The measurement was made at a forward current of 20mA; the luminous flux was 9.4 lumens; the color temperature was 4,600K.

To put this in perspective, a household incandescent bulb has an efficacy of about 14 lm/W and a fluorescent lamp has an efficacy of 60 to 80 lm/W. The new LED even beats a high-pressure sodium lamp, once used for lighting of roadways and parking lots because of its very high efficacy of 132lm/W, but now largely abandoned because of the ugly yellow illumination it produced.

The structure of the new LED is complicated, reported the Nikkei Business Daily, and Nichia still must develop practical methods of manufacture. The company said it does not know when it will begin producing the new device, but a related device that produces 100 lm/W is scheduled for April ‘07 availability, Nikkei said.

The very high efficacy of the new generation of white LEDs is opening (or will soon open) high-volume applications such as LCD backlighting, home and office lighting, and automobile headlights. Switching from current lighting sources to the new highly efficient LEDs would produce enormous global power savings, which has captured the imagination of environmentalists, power authorities, and government agencies around the world.

Partly as a result of this and more traditional competition, makers of LCD backlights are scrambling to make sure they have adequate supplies of LEDs for small-display BLUs and the ramp-up in LED BLUs for larger LCDs that has already begun, initially for notebook PC displays.