Lighting the Way for LEDs

When it comes to energy efficiency and long life, lighting experts consider light-emitting diodes—better known as LEDs—to be a very promising technology. However, these solid-state lighting systems that convert electrical energy directly into light must first overcome a number of technological and market hurdles before breaking into general lighting applications.

"The potential for LEDs is huge, but right now they are not so competitive, except in low-wattage applications," explains Jeff McDonald, a lighting consultant with McDonald Consultants in University Heights, Ohio. "Before moving into task and general lighting, [LED] cost, efficiency, color rendering and color temperatures have to be addressed."

In an effort to tackle these obstacles, the Lighting Research Center—a research and education center dedicated to lighting—at the Rensselaer Polytechnic Institute, Troy, N.Y., recently launched a number of LED programs in partnership with government and industry.

"The technology is quickly developing, but hasn't been integrated yet," states McDonald. "Therefore, anything that helps with the integration of LEDs into lighting applications and lighting fixtures is a good thing."

One such effort is a collaborative research project where LRC researchers are taking a semiconducting element being developed by researchers at the University of California at Santa Barbara (UCSB) and attempting to integrate it with optics and electronic controls.

One of the innovative elements being utilized in this three-year, $3 million research project—underwritten by the U.S. Dept. of Energy—is a gallium nitride-based vertical cavity surface-emitting laser. It is hoped that this design feature will help improve light extraction within solid-state lighting systems, as LEDs tend to trap most of the light they produce.

"The challenge for the LRC is to take these laser-like devices created by UCSB and develop a light fixture suitable for illumination purposes," explains Dr. Nadavarah Narendran, LRC's director of research.

Narendran also points out that LRC researchers will have the challenge of packaging the LEDs because the materials typically used to do the job tend to yellow over time, further compromising light output.

"We are working with leading polymer chemists at Rensselaer to develop suitable, non-yellowing polymers that can be used to encapsulate these new semiconductors," he says.

Another LRC initiative is the formation of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST). The directive of this alliance—comprised of solid-state lighting manufacturers and government agencies—is to promote LED technologies through research, demonstration and education.

For example, a recent LRC program—the LED Lighting Institute—brought together a few dozen lighting specifiers, lighting fixture designers and manufacturers for a two-day training program addressing how to:

• Incorporate LEDs into architectural lighting fixtures.
• Develop optical components that will best take advantage of the small size and compact beam spread of LEDs.
• Design lighting applications using LEDs.

For more information about LED initiatives undertaken by the LRC, visit www.lrc.rpi.edu.