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Tiny LEDs grow into mighty theatrical lights

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As light-emitting diodes move toward the brightness of incandescent light bulbs, they are developing heat buildup, a problem that has long plagued their well-established rival.

But this week, Lamina Ceramics will introduce an LED array with heat-reduction technology that allows it to be as bright as a theatrical light without risking an electronic meltdown.

The light engine, as Lamina calls its disk-shaped product, is based around a new generation of high-powered light-emitting diodes developed by other companies. Lumina's array lacks the efficiency of the best traditional light sources and, with a price tag in the thousands of dollars, is also vastly more expensive. But the company says the technology is an important step in taking light-emitting diodes from keychain flashlights to the largest of lighting jobs.

"The problem people were having in taking advantage of these new bright LEDs was the packaging," said Taylor Adair, the president and chief executive of Lamina, which is based in Westampton, N.J., and is a spinoff of the Sarnoff Corp. "Now we have a solid-state lamp that produces enough lumens to be able to open up new lighting opportunities."

By Lamina's measurements, the disk, which is about 5 inches in diameter and uses hundreds of LEDs, produces 13,300 lumens of light. The company says this is about 10 times the brightness of any solid-state light previously demonstrated. The large metal-halide fixtures commonly used to light grocery stores, by comparison, generally emit 10,000 to 20,000 lumens.

Contrary to common wisdom, all light-emitting diodes produce heat. Until recently, however, LEDs, from the smallest ones on power switches to those on signs in Times Square, were designed to be viewed directly, reducing their energy requirements and heat output. The new high-output LEDs, however, are much brighter, allowing them to provide general illumination by being aimed at objects rather than viewers' eyes.

"You can't look at these ones," said Nadarajah Narendran, the director for research for the Lighting Research Center at Rensselaer Polytechnic Institute in Troy, N.Y. "You'd go blind."

But that brightness means each of the high-output diodes, which typically measure 1 millimeter in diameter, also have a power requirement of 1 watt to 5 watts.

"One watt can get very hot if you don't put it on a heat sink," Adair said. Of course, in an array with hundreds of light-emitting diodes, the heat problem is all the greater.

Once a light-emitting diode heats up beyond 140 degrees Celsius (284 Fahrenheit), Narendran said, "all sorts of bad things happen inside." Eventually, the diode switches from producing heat and light to just heat. The diodes self-destruct long before reaching temperatures that would make them fire hazards.

The most common solution for preventing heat problems is to bundle one to three light-emitting diodes in a plastic, metal and silicon package, known as a heat sink, that dissipates their heat. But the size of those heat sinks means that any array made up of encapsulated LEDs quickly becomes excessively large for practical applications.

The new solution to the heat problem came about as an indirect result of Lamina's primary goal of selling a technology developed by Sarnoff, its parent at the time, to companies that needed to dissipate heat in devices that use microwave frequency radio signals. A little more than a year ago, Adair said, Lumina discovered that its technology could also resolve the problem of the light-emitting diode as well.

Rather than packaging a few diodes into separate heat sinks, Lumina can bond hundreds of them to a single large heat sink that uses fused layers of metal and ceramic to carry the unwanted energy safely away. That allows Lumina to squeeze more diodes, and thus more light, into every square inch of an array.

One drawback, which engineers say can be reduced with further improvements in LEDs, is the array's poor energy efficiency. It requires 860 watts of energy. By comparison, metal-halide lights in stores producing a comparable brightness use 150 watts to 200 watts of power, Narendran said. The conventional bulbs, however, are much larger and emit an unpleasant blue-tinged light.

Then there is the price, which Adair said is largely determined by the cost of high-output LEDs. Lamina plans to sell its arrays to other companies that manufacture lamps. A single Lumina disk will cost about $4,900, although there are substantial discounts for large orders.

For that reason, Lumina's first array is made up of red, green and blue LEDs, allowing it to change instantly among any of 16 million different color possibilities. The company hopes that ability and its compactness will generate a following in theatrical lighting where unusual light fixtures commonly sell for thousands of dollars.

Although Lamina's creation is unusually large and bright, it is not the only array that offers a high density of LEDs. This month, Lumileds Lighting, a maker of high-output LEDs based in San Jose, Calif., introduced a technology that reduces heat problems by combining diodes that have improved thermal efficiency with a metallic heat sink. It is being marketed as a tiny 40-lumen flash for cell-phone cameras.

Jason Posselt, Lumileds' director for product marketing, said the company was developing larger variations for general illumination.