Lighting expert shares research and advice on LEDs
April 21, 2015
The Toronto section of the Illuminating Engineering Society of North America (IES) hosted a speaker from New York at its lunchtime series on April 15. The event was part of celebrating 2015 as the International Year of Light.
Dr. N. Narendran is director of research at the Lighting Research Centre at Rensselaer Polytechnic Institute in Troy, New York. Launched 28 years ago, the centre is a 30,000 square foot research facility with 35 faculty and staff devoted to lighting. They work in three areas: technology, human factors, and design, and have a strong education mandate: “There’s no point in doing research if it’s a secret,” said Narendran.
Within the Lighting Research Center Narendran leads a program dedicated to LEDs. Known as the Alliance for Solid-State Illumination Systems and Technologies, or ASSIST, it collaborates with manufacturers and publishes guidance for the industry based on their research.
Narendran noted that since the first commercial-type LEDs (light-emitting diodes) were developed in the mid-1990s, the technology has “transformed the lighting industry to a great extent.” LEDs, have made the shift from research to mainstream much more successfully than other new technologies such as fuel cells, he pointed out.
He described three areas of research at the Lighting Research Centre that are yielding interesting results. First was in the area of finding a way to accurately specify colour with LED lighting. The standard measures CCT (correlated colour temperature, which measures light warmth or coolness) and CRI (color rendering) are acceptable for many applications, but when it comes to special needs such as in retail food stores and sometimes medical applications, they recommend balancing the CRI with a another metric called “gamut area index” or GAI. The GAI measures the colour saturation as well. He said that around the world lighting standard committees are looking at combining CRI and GAI for expressing colour fidelity.
Another topic he covered was parking lot lighting. Here LED research has shown that what’s important for giving people a sense of security at night is not so much having high illumination levels, as having uniform levels of light. “When the illumination is uniform, perceptions of how good the lighting is and how safe people feel reach high ratings at much lower light levels,” he said. Knowing this, lighting designers can achieve energy savings. The researchers have found the same perception of safety with 9 lux and 3:1 ratio of uniformity, as with 40 lux and a 10:1 ratio of uniformity.
Lastly, Narendran spoke about the testing of luminaires, or light fixtures. He said that early testing of heat strain in LED luminaires was inadequate because it was done on a fast cycle, turning the power on and off in seconds. Although LEDs themselves stay cool, other elements in the fixture heat up over time he said, so a true test would reflect a more realistic scenario and leave the lamp on for three or four hours.
The Lighting Research Center’s “ASSIST recommends” publications are on a range of topics, including general lighting, outdoor lighting, flicker, and dimming. Some are technical and some are more about applications, said Narendran.