Mr. Zhi-cong Bao Profile

Zhi-cong Bao

at Tsinghua University

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Proceedings Article | 20 August 2013 Paper

The design of freeform surface lens for LED lighting system

Zhi-cong Bao, Jun Zhu, Si-si Xiong, Guo-fan Jin

Proceedings Volume 8913, 89130T (2013) https://doi.org/10.1117/12.2033282

KEYWORDS: Light emitting diodes, Light sources and illumination, Lens design, Light, Spherical lenses, Differential equations, LED lighting, Light sources, Optical design, Luminous efficiency

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LED has many advantages, such as high luminous efficiency, small size, low-voltage DC drive, etc. so it has been widely used in many lighting situations. But in certain circumstances, such as uniform illumination requirements in the micro-display projection system, because LED has an analogous Lambertian radiation distribution resulting in its non-uniform light intensity, the secondary optical design should be done to achieve the specific illumination requirements. In this paper, a freeform surface lens is designed to obtain a square area with uniform illumination on the target plane with LED: Firstly, based on the law of conservation of energy, the source-target light energy mapping relationship between the incident plane and the target plane is achieved. Secondly, according to the vector form of Snell’s law, the differential equations of the freeform surface are established. Finally, in order to solve the problem of surface discontinuity during the progress of designing the lens, the process of solving the differential equations is described in detail and the integrability condition is introduced to modify and adjust the points’ position of freeform surface, thus reducing the errors accumulating during the progress of numerical calculation and improving the continuity of the freeform surface. By simulation, the continuity of the freeform surface and the uniform illumination improve a lot, so it is validated that the results meet the requirements and the design method using integrability condition can improve the continuity of the surface and lighting uniformity of the lighting system.

Proceedings Article | 20 August 2013 Paper

Design of freeform surface lens for LED of random light distribution in road lighting

Si-si Xiong, Jun Zhu, Zhi-cong Bao, Guo-fan Jin

Proceedings Volume 8913, 891315 (2013) https://doi.org/10.1117/12.2041203

KEYWORDS: Light emitting diodes, Light, Light sources and illumination, Roads, Optical design, 3D modeling, LED lighting, Partial differential equations, 3D applications, Light sources

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Previous secondary optical designs, however, have approximated the LED light distribution curve as a Lambertian distribution which is unable to suit all custom sources. In this paper, a freeform surface lens is utilized to redistribute the light rays emitted from a LED device with a random light distribution curve in order to effect a prescribed illumination distribution on the target area. A mapping relationship is also established between the spatial light intensity distribution of a light source and the rectangular uniform illumination used for road-going cases. A set of first-order partial differential equations is deduced according to Snell’s Law and the Law of Energy Conservation. A numerical solution is obtained through MATLAB software, and freeform surface data of the secondary optical lens is recorded to aid in modeling the freeform surface lens. Simultaneously, an analysis and comparison of different differential algorithm and mapping methods is carried out in order to solve the differential equations and designate the most superior mapping relationship. With the help of 3D software, a 3D model of the freeform surface lens is established, and Light Tools software is employed to simulate the effects of illumination. In this model, the light distribution curve of the LED source is described as an eighth-order polynomial. According to the simulated results, a 10m height, 40m×40m road uniform illumination is realized by the secondary optical design. The energy efficiency and uniformity of this illumination is 99.7% and 91.52% respectively. This method of secondary optical design is easy to operate and can be applied to any other lighting systems with random LED sources.

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