| As "green energy", the LED road lighting products have occupied part of the market at home and abroad, and it will enlarge in the following years. However, there are still two problems during the practical design. First of all, secondary optical design was conducted by traditional method. Some disadvantages involving in this kind of method, that is it rely on the experiences of engineer and it is time and energy-comsuming and also in low design efficiency. Besides, some of LED road lighting products from the market have poor thermal management performance, this will cause seriously influence on the optical extraction of LED. According to these actual problems, in this paper, differential equation method was applied to deduct the free-from surface equation so as to design lens for lambertian LED, whose viewing angle is 120 in degree. This method can not only avoid the blind design but also guarantee the precise of lens. By solving the equations to get the numerical solution, the data of free-form surface was achieved directly. In order to approve the feasibility of this algorithm, the lens model was imported to optical software to conduct raytracing. The simulation of thermal management was based on thermal analysis software. After orthogonal experiment, a model structure with better thermal radiation performance and less material was conducted. For the purpose of approving whether the optical and thermal design in this paper are feasible, a street lamp was made. The equipment and compoment of the street lamp were bought from market.The lens designed in this paper is suitable to be installed on those LEDs who were distributed on a plane. The reason for this is that light from LED was refracted by lens and then re-distributed evenly in the effective lighting area. Therefore, the average illuminance of effective lighting area is easily altered by simply adding or substracting number of LEDs on the plane. This kind of design can simplify the structure of radiator a large degree. In that case, it is also helpful for manufacturethe radiator model. The experimental results indicate that when the street lamp is installed in 10m heigh, the uniformity of illumiance in 35×10m2 effective area is 0.5 and 0.41. The total power of street lamp system and LEDs are 184.5W and 163.3W respectively. The lens designed in this paper was also simulated in DIALUX, and the results are as follow. The uniformity of 30×10m2 and 35×10m2 effective area are 0.78 and0.645 respectively, which are higher than that of standard by 95% and 61.25%.From the thermal management aspect,the junction temperature of LED was maintaned under 80℃after street lamp working nonstop for 7 hours with the 24.5℃environment temperature. This junction temperature value is far less than that maximum limited temperature of LED PN junction. The optimized medel in this paper have superior performance than that of the prototype of the street lamp system. At the same invironment, the junction temperature of LED decreased by 4.01℃only with 71.6% the weight of prototype model. The new model can save heatsink material effectively.In this paper, mathematical algorithm was applied so as to get the data of free-form surface, it is able to improve design efficiency of lens. Based on CAD, the thermal design and analysis was conducted effectively. All of these are meaningful for development of road lighting products.
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