18 December 2012 Investigation of the design space for low aspect ratio LED collimators
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Collimators for spot LED lamps have to meet stringent requirements like high efficiency and on axis intensity, good beam control, color and position mixing, low cost, and a low aspect ratio to enable compact devices with sufficient space for drive electronics and cooling. To meet such requirements only very few optical architectures are routinely used, namely Fresnel lenses, parabolic or aspheric reflectors, and TIR lenses, often called Photon funnels. Collimators make use of five different deflection mechanisms, namely refraction, total internal reflection, metallic or metallic like reflection, scattering, and diffraction. Light, when travelling through a given collimator type undergoes a characteristic sequence of deflections but many collimators exhibit different paths where portions of the light undergo different deflection sequences. In this paper we illustrate the design space for collimators for a single Lambertian LED or LED array source located on the optical axis under the boundary conditions of low aspect ratio, rotational symmetry and minimum Etendue dilution. All possible optical architectures with up to 4 deflections are mapped out in terms of paths of distinct deflection sequences. The important characteristics of deflection sequences are investigated. For a given collimator, the deflection paths involved allows predicting efficiency, on axis intensity, and compactness. Additionally the beam shape as well as position and color mixing capabilities can be estimated from the influence of the deflection sequence on pinhole image rotation and distortion. Such results are compared to raytrace results for some designed collimators of standard and uncommon architectures.
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O. Dross, "Investigation of the design space for low aspect ratio LED collimators", Proc. SPIE 8550, Optical Systems Design 2012, 85502M (18 December 2012); doi: 10.1117/12.980512; https://doi.org/10.1117/12.980512

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