Lens sharpens LED light

Researchers are developing powerful new optical components

A new optics component (bottom left) directs the light from light-emitting diodes (right) to where it is needed. © Fraunhofer IPT
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Light-emitting diodes radiate extremely energy-efficient. However, they can not compete with light bulbs - so far. Because a new plastic lens should change that now: It bundles the LED light and steers it specifically where it is needed.

A single watt LED gives about the same optical performance as a one hundred watt bulb. However, if high light output is required, the small light sources are not yet the lighting of choice.

However, the novel optical component developed by Fraunhofer researchers now bundles the light in a desk lamp, for example, so that only a large area of ​​A4-sized space in the center of the table shines brightly. The LED illuminates the required area evenly, everything outside remains in the dark.

"A light-emitting diode is a point light source that emits light in a large, uncontrolled area, " says Christian Wenzel from the Fraunhofer Institute for Production Technology IPT in Aachen. "With special lenses, we use the light one hundred percent where it is needed, and thus increase the efficiency of the LEDs. The light spot thrown by the light source does not run outward, but has a sharp edge. "

Good and cheap

The basis for this light guide is a free-form surface optic - a plastic lens whose geometry can be freely designed. "The lenses are cast using an injection molding process. The two tool halves, which serve as a mold, must be aligned once highly precise - the accuracy is a few micrometers, and thus less than a tenth of a hair diameter. Once the tools have been tared, the lens can be produced inexpensively in large quantities, "says Wenzel. display

The researchers at IPT have optimized the entire process chain, from the planning of the optics through the manufacture to the inspection. "This is so far unique in Europe, " says the expert.

Plastic shrinks on cooling

A challenge here: the plastic, which is given hot into the mold, shrinks on cooling - the finished lenses are therefore slightly smaller than the shape pretends. The researchers take this effect into account by repeatedly improving them step by step - to a few micrometers.

When the lenses are finished, the scientists check them: To do this, the researchers project a striped pattern onto the lens. Due to the distortion of the stripes can be concluded that the curvature, inclination and shape of the lens.

(idw - Fraunhofer-Gesellschaft, 05.05.2008 - DLO)