Polycarbonate collimator lenses
Light-emitting diodes (LEDs) use little energy and have a long service life. Applications include street lamps, lighting in buildings, advertising billboards, automotive lighting and liquid crystal displays. Polycarbonate is now finding use as a material for the focusing optics for these LEDs.
In cooperation with Light Prescriptions Innovators (LPI), Altadena/USA, Bayer MaterialScience AG has succeeded in producing PC collimator lenses. These lenses bundle the light from LED automobile headlamps and direct it onto roadway. This means that all of the light can now be focused by a single component, while classical lens systems required several components for this purpose.
The "RXI" collimator lens designed by LPI exhibits complex free-form surfaces and extreme changes in wall thickness. For this reason, the lenses are produced in a two-cavity mold by means of double-layer molding. A preshot is initially molded in the first cavity and then overmolded in the second cavity to yield the final shape of the part. By using this approach and a special temperature control technique, it is possible to produced lenses with very good surface quality. Sink marks that have an adverse effect on the optical efficiency of the lenses are thus avoided.
As the material for LED focusing optics, polycarbonate offers several advantages over PMMA, which is also clear. With a heat deflection temperature of up to 130°C, it can reliably withstand the maximum operating temperatures of LEDs. Because its index of refraction is greater than that of PMMA, the lenses can be thinner. Thanks to its toughness, guides, housing elements and fasteners such as snap fits can be incorporated into to lenses without difficulty. The lenses are rugged and unbreakable. Short cooling and cycle times translate into increased productivity, especially when optics with free-form surfaces are involved, since they typically have wall thicknesses in excess of ten millimeters.
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