Scientists at the Lighting Research Center (LRC) of Rensselaer Polytechnic Institute have developed a method to boost the amount of light from white LEDs without using more energy. The new technique is called scattered photon extraction or SPE.

Commercial white LEDs combine a blue to ultraviolet LED with a phosphor comprised of rare-earth compounds. The phosphor glows brilliant white when struck by high-energy photons from the LED. However, light emitted by the phosphor scatters in all directions. Half of it is diverted back into the LED where it is lost to absorption.

Dr. Nadarajah Narendan and his research group moved the phosphor coating away from the LED semiconductor material. They then reshaped the LED lens geometry to redirect more white-light photons from the phosphor out of the LED assembly. Prototypes of the new SPE LED design produced 30 to 60% more light output and luminous efficiency (light output per watt of electricity).

The lighting industry has set a target for white LEDs to reach 150 lm/W by the year 2012. Under certain operating conditions, the SPE LEDs hit more than 80 lm/W. Compact fluorescent lights reach 60 lm/W while standard incandescent lamps provide only 14 lm/W.