26 June 2017 Component-level test of molded freeform optics for LED beam shaping using experimental ray tracing
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Abstract
Due to the high demand of LED light sources, the need to modify their radiation pattern to meet specific application requirements has also increased. This is mostly achieved by using molded secondary optics, which are composed of a combination of several aspherical and freeform surfaces. Unfortunately, the manufacturers of these secondary optics only provide output information at system level, making impossible to independently characterize the secondary optic in order to determine the sources of erroneous results. For this reason, it is necessary to perform a component-level verification leading to the validation of the correctness of the produced secondary optic independently of the light source. To understand why traditional inspection methods fail, it is necessary to take into account that not only errors due to irregularities on the lens surface like pores, glass indentations or scratches affect the performance of the lens, but also differences in refractive index appear after the compression during fabrication process. These internal alterations are generally produced during the cooling stage and their effect over the performance of the lens are not possible to be measured using tactile techniques. Additionally, the small size of the lens and the freeform characteristics of its surface introduce additional difficulties to perform its validation. In this work, the component-level test is done by obtaining the ray mapping function (RMF) which describes the deflection of the light beam as a function of the input angle. To obtain the RMF, firstly a collimated light source is held fix and the lens is rotated. Thus, a virtual point source is created and subsequently by using experimental ray tracing it is possible to determine the ray slopes, which are used to the retrieve the RMF. Under the assumption that the optical system under analysis is lossless and considering the principle of energy conservation, it is possible under specific conditions to use this new approach to obtain the output of the complete set, composed of light source plus secondary optic. Thus, for different LED models, combining their radiation pattern with the RMF allow us to obtain the resultant modified radiation pattern. By following this procedure, the correct functionality of the secondary optic is verified independently of the light source. This method brings the opportunity to the final product manufacturer of defining fail regions over the desired resultant output radiation pattern as a combination of different LED sources and then verify if the secondary optic fulfill the requirements.
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Gustavo Gutierrez, Gustavo Gutierrez, David Hilbig, David Hilbig, Friedrich Fleischmann, Friedrich Fleischmann, Thomas Henning, Thomas Henning, } "Component-level test of molded freeform optics for LED beam shaping using experimental ray tracing", Proc. SPIE 10329, Optical Measurement Systems for Industrial Inspection X, 1032930 (26 June 2017); doi: 10.1117/12.2270247; https://doi.org/10.1117/12.2270247
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