Leaving the Lights on

A tour through a center that tests CFLs, LEDs, and human health

Jeremy Snyder: "You used to go into the hardware store or grocery store, your lightbulb at home is burnt out, so you just reach on the shelf and grab another one. And now the choices are getting slightly more complicated, and people are going to have to start making some evaluations."

Energy-efficient compact fluorescent bulbs and light-emitting diodes are starting to replace incandescent lights around the world. But their complicated electronics mean they won't perform exactly like their predecessors. Here, at the Rensselaer Polytechnic Institute's Lighting Research Center, in Troy, N.Y., researchers run a new generation of bulbs through a gauntlet of different tests. They want to help consumers make more informed lighting choices.

Jeremy Snyder: "Sure, you could say, ‘Take out whatever lamp you have now and put in the most efficient light source.' Well, if that doesn't work for the people in that environment, then it's not going to work at all. People are going to switch back."

Jeremy Snyder works in this nationally accredited laboratory. In some ways it's a lightbulb infirmary. Computers connect to large racks of lamps. They can monitor bulbs' vital signs, like power, and sometimes, time of death. Each technology has its own weaknesses. For example, CFLs don't live as long when they're switched on and off repeatedly. This stresses the lamp's electronics.

CFLs use a fraction of the power that incandescent bulbs require, but they cost more. To make up for that price tag with energy savings, CFLs have to live long enough.

Jeremy Snyder: "We operate the lamps for a number of hours based on their rated life, and that's done on these racks."

The lab can keep the lamps lit for extended periods—100 hours, 1000 hours, and 40 percent of the lifetime listed on the package. That can mean running the lights for months on end, in cycles, of 3 hours on and 20 minutes off. Besides monitoring for burnt-out bulbs, these lifetime tests determine light output in lumens.

Jeremy Snyder: "You want to know the total amount or the integrated amount, and that's why you use an integrating sphere."

Integrating spheres have a white interior to reflect light in all directions so researchers can measure the total light output of a lamp. A chilled-water cooling system surrounds one of these spheres. Researchers conduct many of these tests at 25 degrees Celsius and some high-temperature lifetime testing at 55 degrees Celsius.

Nadarajah Narendran: "Yeah, we got from baby spheres to grandpa spheres."

Nadarajah Narendran: "This is the setup where the LEDs are being burned, and every so many hours we'll take it and put it in the integrating sphere."

Nadarajah Narendran is director of research at the Lighting Research Center. In a small cabinet, he tests light-emitting diodes.

Nadarajah Narendran: "You don't overpromise anything. That's the pitfall of every technology that comes out. I can go on and on about how electronic ballasts did it, CFLs did it. Once you set the expectation, if it doesn't meet it, people are going to get disgusted with it and say, look, this is not doing what it's supposed to do."

Narendran's team helps to develop new testing procedures that more accurately reflect the conditions an LED might experience outside the laboratory. As an example, he points out that enclosed lighting fixtures can prove fatal for fluorescents and solid-state lighting.

Nadarajah Narendran: "For an incandescent or a halogen, it doesn't matter, because even if you put it into a recessed scenario, the heat doesn't bother it. With LEDs—remember, I said heat bothers it, so we have seen scenarios where the light could be 30 to 35 percent lower. And in these situations the life gets shorter, too, when the temperature goes up."

Nadarajah Narendran: "So here are all the coffins. There, some of them actually died in about 3000 to 4000 hours, and here is another example where the light is now blue in color."

Narendran's laboratory also works to make these lights perform better. In 2005, his team noticed that traditional LED designs wasted light: Much of the photons emitted from the diodes' phosphor coatings never escaped the LED package. By rearranging the device's internal components—moving the phosphor away from the diode—his lab made the devices shine up to 60 percent brighter.

But even the best-engineered light source is only as good as it looks to the people who use it. So the center also studies humans. Mariana Figueiro, who leads the center's Light and Health Laboratory, uses two devices, called a Daysimeter and a Dimesimeter. These can measure the light that a person sees. Her lab has published studies on how lighting choices can influence school children, Alzheimer's patients, and night-shift workers. She correlates light measurements with biological ones, such as the body's levels of the hormones melatonin and cortisol. She's even investigating alternatives to outdoor sunlight—as the center's cofounder, Russ Leslie, is happy to demonstrate.

Russ Leslie: "These are different ways to put different wavelengths of light in people's eyes. So these are light goggles."

Associate director since 1988, Leslie says one of his favorite parts of the job remains the variety of technologies that he has the chance to work on, as well as the people who rely on the center's results.

Russ Leslie: "In a given week we may be talking to people that are regulating the power grid, people that are trying to use lanterns so people can see better in Africa and charge them up with solar, to submariners who are trying to have a better circadian cycle. It's different every day."

For IEEE Spectrum, I'm Joseph Calamia.

NOTE: Transcripts are created for the convenience of our readers and listeners and may not perfectly match their associated interviews and narratives. The authoritative record of IEEE Spectrum’s audio programming is the audio version.

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