Study On The Design Of LED Illumination System Based On Freeform Surface

Various advantages can be expected when using Light Emitting Diode (LED) as the light source to build up the illumination system: including reduced energy cost, lower pollution, miniature, and longer lifetime. But the layout and the luminance distribution of the LED are so different from the traditional sources that the conventional illumination systems are not suitable for LEDs. The Freeform Surface can simplify the structure of the illumination system and increase the degree of design freedom. Meanwhile, the Freeform Optical Surface can also get the specific light distribution freely and improve the performance. It has potential application prospects in the mini-type LED illumination system. So it is meaningful and necessary to develop the research in this field.This thesis introduces a new method to design Freeform optical surface for uniform illumination with high light usage efficiency. By Snell's Law and the knowledge of differential geometry, the differential equations are given to donate the relationship between the directions of normal of freeform surface and input/output ray vectors. Numerical method is then used to get the result. Further more, two optical models for uniform illumination are discussed, and by embedding the source into the refractive Freeform Surface, 100% efficiency is achieved in theory. Some practical experiments are discussed later in the thesis: the Freeform Surface Lens is processed by using perfusion method, and its performances in DLP system are also tested.In the beginning of the thesis, typical kinds of the illumination systems are introduced including the background, category and the optical structures. Then the development of LED is shortly presented, followed by the introduction about the development and advantages of Freeform Surface.The second chapter is about basic knowledge related to this thesis. Firstly is the history and the basic theory of non-imaging optics. Then the method of designing Freeform Surface Lens by using differential geometry theory is discussed in detail and the differential equations are deduced and the results are given by numerical method. The content also includes the introduction of the method of getting 100% radiation usage efficiency and the performances are stimulated by ASAP. Finally how to use this method in other axisymmetric-like cases is discussed.The third chapter gives some Freefrom Surface design examples based on the theories mentioned in Chapter 2.The forth chapter lists all possible methods to process practical Freeform Surface and their characters are compared. Especially, the whole process of perfusion is discussed in detail.The fifth chapter discussed the other problems during building up LED illumination system besides optical ones, including electrical, thermal, and mechanical problems. Related testing methods and the final performances are also shown.At the end of the thesis, the conclusion and future research direction are given.