Catadioptric freeform optical system design for LED off-axis road illumination applications

Abstract

Abstract:The aim of this paper is to develop a new composite structure of catadioptric optical system containing both freeform refractive surface and freeform total internal reflective (TIR) surface for LED road illumination applications. The role of freeform refractive part is to generate the shifted general rectangular illumination pattern to optimally match the shape of the road surface. The application of TIR mechanism is aimed to control the stray light in the sidewalk direction of the road luminaire and maximize the efficient energy efficiency. In this paper, we use the "double pole" ray mapping technique to design the refractive optical surface and the θ-φ coordinate ray mapping technique to derive the freeform TIR surface. The simulation shows that the novel catadioptric design has relatively high collection efficiency, thus high average illuminance level inside the effective illumination area. This lens also has good control of stray light on the backside of the road luminaire.

Multi-surface catadioptric freeform lens design for ultra-efficient off-axis road illumination

“…The results show superior optical performance and ultra-high collection efficiency compared to our proposed result in Ref. [28] for off-axis road illumination.…”

“…In the previous publication [28], the authors employed the composite ray mapping method [14] which combined the "double pole" ray mapping technique [15] and the θ-φ ray mapping technique to establish a diffeomorphism so that the transformed irradiance distribution matches the target distribution. Furthermore, the Euler's iteration algorithm is implemented to construct the freeform exit surface and the freeform TIR surface in [28]. In this paper, we completely updated the design method and lens configuration for preferable optical performance.…”

“…In this section, we demonstrate the method to determine the analytic entrance surface and TIR surface. In our previous publication, the entrance surface is a simple sphere and the exit surface of TIR part is a plane which is zero degree of design freedom [28]. In this paper, we increased the design freedom by setting analytic entrance and TIR surface.…”

Design of Freeform Illumination Optics

“…This is an inverse problem, the number of freeform surfaces which should be used depends on the design requirements. The design methods of freeform illumination optics can be broken into two groups according to the influence of the spatial or angular extent of an actual light source on the design: zero‐étendue algorithms based on ideal source assumption (point light sources or parallel light beams) and algorithms for extended light sources . When the influence of the spatial or angular extent of a light source can be ignored, the light source can be considered as an ideal source (a point source or a parallel beam) and the inverse problem can be converted into a well‐defined mathematical problem.…”

“…When the influence of the spatial or angular extent of a light source can be ignored, the light source can be considered as an ideal source (a point source or a parallel beam) and the inverse problem can be converted into a well‐defined mathematical problem. The formulization of this inverse problem can be done in the ray mapping method . A key step in the ray mapping method is to find a ray mapping such that the calculated normal field can satisfy the integrability condition, leading to a system of a first order partial differential equations .…”