Design analysis of 3d printed internal cavity lens for lighting applications

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Udage, Akila, Shan
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LED lighting systems consist of an LED light source and several subsystems, including optical, electrical, and thermomechanical components. The optical subsystem uses reflective, refractive, or a combination of reflective and refractive components to transfer the luminous flux from the LED light source to the target area to satisfy the application’s light level and distribution requirements. A refractive optic or lens is a transparent material with a given index of refraction and a shaped external surface that redirects the incoming beam. Refractive optics exposed to the application environment can cause lumen depreciation when dust and dirt accumulate within the crevices of its contoured external surfaces. Such light loss can cause the secondary optics to become less effective over time. Furthermore, lenses with non-flat external surfaces pose challenges when assembling LED lighting systems. An optic with internal refractive cavities and flat, smooth external surfaces can reduce such problems. Therefore, this dissertation study aims to investigate the design strategy and manufacturing method of internal-cavity flat optics for use in LED illumination systems. Although many studies have examined lens design methods for external refractive surfaces, no study has proposed design strategies for internal cavity lenses with planar external surfaces. In this dissertation study, a novel design method was investigated and analyzed for creating flat lenses with internal cavities. The internal refractive cavity is created between two internal freeform surfaces that are formed based on the light-energy mapping method and that consider the edge ray principle and Snell’s law. The study objectives of this research project were established by understanding the knowledge gaps in the areas of freeform lens design algorithms for designing internal cavity lenses and manufacturing methods for such lenses. First, an algorithm was developed for designing the surfaces of the internal refractive cavity by extending the freeform design method for producing a circular symmetric light distribution on a target plane. Later, this algorithm was advanced to achieve non-circular symmetric distributions as well. In both cases, a mathematical relationship was formed based on geometric optics to design the internal refractive surface geometries. Defined surface geometries were used to generate the 3D model of the internal cavity lens. The design method was validated using the results from a Monte Carlo ray-tracing simulation study and a laboratory experiment that analyzed the output beam of the 3D-printed internal cavity lenses. Tolerance analyses were performed to assess the effects of different design parameters on the beam quality and lens efficiency. The initial ray-tracing results demonstrated that the proposed lens design method can construct internal cavity lenses with optical efficiencies of 83% and 80%. The calculated uniformities were 1:1.9 and 1:2.3 during the ray-tracing simulations. The experiment results showed that for the two 3D-printed flat internal cavity lenses that formed the different beam patterns, the optical efficiencies were 72% and 70% and the beam uniformities were 1:2.2 and 1:2.2 with the material and 3D printer used in this study. The lower optical efficiencies in the experimental results could be mainly due to Fresnel and scattering losses incorporated with the 3D-printed lenses. To the best of the author’s knowledge, the proposed internal cavity lens design strategy-that is, by simultaneously designing a pair of internal refractive surfaces by extending the freeform method has never been studied before. Therefore, the new knowledge contribution to the field of optics through this dissertation study includes a design method for a flat internal cavity lens and the manufacturing of such lenses. The author believes this study will open up a new field of exploration for the concept of internal refractive cavity lenses. Moreover, it will provide information on how to use additive manufacturing optics to develop new optical designs that add value to a wide range of applications.
December 2022
School of Architecture
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Rensselaer Polytechnic Institute, Troy, NY
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