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Component Channels LED Light

Photonics.com
May 2008
AACHEN, Germany, May 19, 2008 -- LEDs are more energy-efficient than light bulbs, but fall short when it comes to light output. But a new optical component could change that by concentrating LED light like a spotlight and directing it precisely where needed.

A 1-W LED delivers roughly the same optical output as a 100-W light bulb, making the LED more energy efficient. But the tiny light sources are not currently the preferred means of illumination when a high light output is required. Researchers at the Fraunhofer Institute for Production Technology (IPT) in Aachen have developed an optical component that can concentrate the light like a spotlight. When used in a a desk lamp, for example, the light can be channeled so that only a spot about the size of a sheet of paper (DIN-A4-sized) in the middle of the table is brightly and evenly lit, while everything else stays in the dark.
FraunhoferComponent.jpg
A novel optical component (bottom left) channels the light from LEDs (right) precisely where it is needed. (Image copyright ©Fraunhofer IPT)
“A light-emitting diode is a single-point light source that emits light in a large, uncontrolled area,” said Christian Wenzel, PhD, head of department at the Fraunhofer Institute for Production Technology (IPT) in Aachen. “We use special lenses to direct all of the light to the place where it is needed, thus increasing the efficiency of the LEDs. The spot of light created by the light source does not therefore fade out at the edges, but has a sharply defined edge.”

This channeling of light is based on a free-form system of optics -- a plastic lens whose geometry can be shaped as needed, the researchers said, with the lens manufactured at the institute.

“The lenses are cast using an injection-molding technique. The two halves of the tool that serve as a mold have to be aligned with extreme precision just once -- they have an accuracy of a few microns, or less than a tenth of the diameter of a hair. Once the tools have been tared, the lens can be manufactured in large batches at low cost,” said Wenzel.

One challenge that had to be overcome was the fact that the plastic, which is inserted into the mold hot, shrinks as it cools, making the finished lenses slightly smaller than when molded. The researchers take this into account by repeated, gradual improvements, to an accuracy of a few microns. When the lenses are finished, the scientists check them by projecting a pattern of stripes onto the lens. The distortion of the stripes reveals the lens curvature, inclination and shape.

The Fraunhofer IPT researchers will demonstrate the entire process, along with optical systems for practical applications, at the Optatec trade fair in Frankfurt, Germany, June 17-20 (Hall 3, Stand D53).

For more information, visit: www.ipt.fraunhofer.de/EN/


GLOSSARY
injection molding
A method of producing high-quality plastic optics in large volumes by injecting the heated, liquified plastic at high pressure into a tooled mold with polished chromium stainless steel inserts to define the optical surface. The plastic solidifies as it cools, and the mold is removed.
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
optical
Pertaining to optics and the phenomena of light.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
plastic lens
A lens made from transparent plastic material. Lenses over 31/2 in. in diameter are usually machined, ground and polished. Smaller lenses are usually injection molded, the mount surrounding the lens often being molded in place at the same time. As an example, a pair of spectacle lenses may be molded with the frame in position.
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