Research On Optical Freeform Surface Of LED Street Lighting

With the continuous improvement of luminous efficiency and declining cost of high-power LED package module, there are more and more applications of high-power LED in general lighting. During the past decade, street lighting had been one of the most popular application of LED lighting. However, in our country, the LED road lighting is still in its initial stage of development. Consequently, we focus our research on the application problem of LED street lighting by use of the design method of optical freeform surface, which is based on non-imaging optics.Freeform surface illumination is an elegant way of lighting, which is remarkably different from the conventional surface illumination, due to its flexible spatial layout and high degrees of design freedom.In this article we introduce a freeform design method based on energy mapping and tangent-plane-iterating method, including a feedback strategy. To improve the design result, we put forward a new freeform constructing method called "improved tangent-plane-iterating". On the other hand, we introduce a novel calculating method, which allow us to take an arbitrary surface as inner surface to dramatically improve the illumination quality.Longitudinal luminance uniformity is a very important index of street lighting. However, the test of luminance is much more difficult than illuminance, which lead to a worrisome situation of our country's road lighting industry. Some road ramp product sold in the market did not meet the national standards CJJ 45-2006. So in chapter 3 we detailedly analyze the relationship of illuminance and luminance on the road surface. To solve a reasonable light distribution pattern, we put forward a new method, by which we only need to solve a set of liner equations to find out light distribution pattern of the road ramp. In chapter 4, we design an asymmetric LED freeform light-distributing-lens to realize the earlier solved illumination pattern. The simulation results shows that by use of this lens, we have a longitudinal luminance uniformity of at least 0.86 at every single lane, which is an excellent compliance with national standards CJJ 45-2006, while other indicators, including illuminance uniformity, threshold increment and surrounding ratio meet the design requirements simultaneously.