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Light of the future

Carla Bleiker
June 26, 2014

A team of German scientists has come up with a new luminescent material for LED bulbs. The phosphor improves energy efficiency and makes this artificial light almost as natural as the sun.

Light diodes. (Photo: German Future Prize, Ansgar Pudenz)
Image: Deutscher Zukunftspreis/Ansgar Pudenz

Wolfgang Schnick knows a thing or two about light quality. Not only has the German chemist researched luminescent materials since 2001 - but shopping expeditions with his wife have taught him first-hand the difference between good and bad light.

"When I go shopping with my wife, she sometimes asks me to go outside with her to look at a dress she wants to buy in daylight," Schnick says.

You've probably experienced it too. The light inside a store can be so distorted that a blue dress can seem black.

But Schnick, a professor of solid-state chemistry, and his team of scientists at the Ludwig-Maximilians-University in Munich have developed a new luminescent material, which could mean this common problem becomes a thing of the past.

They have developed a new luminophore - a chemical compound used in luminescence. Theirs changes the color of light emitted by LEDs (light emitting diodes) in such as way that they believe it has "the potential to revolutionize the LED market."

Mixing light colors

Ever since incandescent light bulbs were ordered off the EU market in 2012, LEDs have been propped up as the best lighting alternative.

They are popular because unlike energy saving bulbs, LEDs light up immediately, without a warm-up phase, and they contain hardly any toxic material.

The problem is plain LEDs only emit one color. But that's not how we like to experience light in day-to-day situations.

Little pots with different colors. (Photo: German Future Prize, Ansgar Pudenz)
The best light is all in the mixImage: Deutscher Zukunftspreis/Ansgar Pudenz

When we read a book on a dark afternoon or look at ourselves in the bathroom mirror first thing in the morning, we expect a white light - and white light is a mixture of many colors.

It is possible to achieve this with LEDs by covering them with a luminescent material.

For white light, an amber-colored luminophore is usually applied to blue LEDs. It is the same principle as applying crepe paper to a lamp to get a fancy red or blue glow.

Some years ago, Schnick's team collaborated with the Philips Lumileds Development Center to develop a material that does just this for LEDs. It's still on the market, used in LED bulbs made by the development center's parent company, Philips.

"Our luminescent material was efficient," says Schnick. "But the industry told us it wasn't good enough."

So the team continued its research.

Approaching sunlight

They have just published their latest findings, detailing a new material that produces a higher quality LED light.

Using the new LEDs, Schnick and his wife wouldn't have to walk outside of a shop to see whether they are looking at a dark-blue garment or one that is black - because the artificial light would be almost as natural as sunlight.

It's all about the color of the light as measured on the color rendering index (CRI).

"The color rendering index should be as high as possible for a good light source," says Schnick. "Sunlight is almost at 100. Current LEDs are at about 80. With our new luminescent material, we get to above 90."

Better efficiency

The new luminophore also promises to make LED bulbs more efficient.

Wolfgang Schnick. (Photo: German Future Prize, Ansgar Pudenz)
Schnick and his team have been finalists for the German Future PrizeImage: Deutscher Zukunftspreis/Ansgar Pudenz

Current LED bulbs use luminescent materials that add too much red to the light. The resulting wavelength is similar to that of an infrared light, one which the human eye can't fully process.

And light we can't process is light we can't "see" - and a waste of energy.

The scientists say their new luminescent material fixes this problem. It adds less red to the color mix and as a result, the LED bulbs are up to 14 percent more energy efficient than current ones.

Light of the future

Johannes Thema, a research fellow at the Wuppertal Institute for Climate, Environment and Energy, says current LED bulbs are about as efficient as energy saving bulbs (compact fluorescent lamps, or CFLs).

But he says LEDs will soon overtake CFLs in efficiency.

Not only this, but the scientists also say energy saving bulbs have a big flaw: they contain mercury.

If CFLs are not recycled properly or if they break, the mercury can leak, posing serious health and environmental risks.

There's no such danger with LEDs.

"I think LEDs are the lighting technology of the future," says Thema.

And Wolfgang Schnick feels the same way.

He says that if all light bulbs in Germany were replaced with his "new LEDs," the country would save about 96 terawatt hours of energy per year.

"That's as much energy," he says to clarify, "as all the nuclear power plants in Germany produce in one year."

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