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.
Highlights
With emerging development of light emitting diode (LED) technologies, LEDs have been revolutionizing almost every aspect of modern life due to their incomparable advantages over traditional light sources, such as long life-time, high energy efficacy, friendliness to environment, good color rendering, and so on [1,2,3,4,5,6]
The factor that the intensity distribution of LEDs follows the Lambertian property limits their applications in our daily life including the road illumination, which generally requires an off-axis rectangular pattern to match the physical shape of road surface
Luo et al focused on achieving a uniform distribution of luminance onto the road surface, where irradiance distribution was not considered, and little discussion was provided for the final illumination pattern and the stray light control in sidewalk direction [11]
Summary
With emerging development of light emitting diode (LED) technologies, LEDs have been revolutionizing almost every aspect of modern life due to their incomparable advantages over traditional light sources, such as long life-time, high energy efficacy, friendliness to environment, good color rendering, and so on [1,2,3,4,5,6]. Many researchers have proposed various ways to design the freeform optics to redistribute the intensity of LEDs to satisfy the actual application requirements [7,8,9,10]. Those freeform lens systems are typically designed for the case where the LEDs are located right above the center of road surface, which is not always true in real applications. Some research considers the off-axis illumination pattern requirement for road illumination application, but the performance is poor with regards to the uniformity and collection efficiency [11, 18]
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