Research On Lighting Design Of Mixed Freeform Surface Based On Refraction And Diffuse Reflection

As a new solid light source,LED has the advantages of high luminous efficiency,low energy consumption and long life,so it has been widely used in various fields of industries and life.Because the characteristics of LED is Lambertian distribution,its illumination uniformity and efficiency are low,and is difficult to meet the strict requirements of industrial and life.Therefore,second-step photometric design is needed to improve its practical value.In order to achieve high efficiency,high radiation uniformity and arbitrary shape target plane,this paper proposes a design method of the cutting lens as the design basis,then irradiance optimization is supplemented by diffuse reflection surface(cutting surface,lofting surface,freeform surface).The method is to plan the shape of the lighting area generated on the target plane,and improve the illumination efficiency under the condition of ensuring the uniformity of the irradiation.Firstly,in order to ensure the shape of the lighting area,we propose a design method of the cutting lens which can precisely align the edge of the lens cutting edge with the boundary of the lighting area.The design method is capable of cutting a lens according to a specific shape of the target plane,and the secondary processing lens can achieve a highly uniform lighting area.This method considers the light source as a point source and mathematically models it by partial differential equation method,energy conservation law,Snell's law and edge ray theory.After that,the equations are numerically solved,and a series of two-dimensional curve are obtained in all directions,which are synthesized into a smooth surface freeform lens by Solidworks.The simulation results show that the method can make the irradiation uniformity of the target surface reach 90%,and the generated rectangular lighting area and triangular lighting area are more similar to the designed shape of target lighting area.Based on the design method of cutting lens,the diffuse surface is introduced into the design of the lens in order to achieve a more efficient rectangular lighting area.For the most common rectangular lighting as an example,this paper proposes a combined lens design method for rectangular illumination,which is composed of a cutting lens and a pedestal.We determined the cutting lens through the shape of the target plane and then applied diffuse reflection material to the partial surface of the pedestal.The diffuse reflection material is used to improve the lighting efficiency of the target plane.The surface of the pedestal is obtained by lofting from the contour of the cutting lens to the contour of plane where the light source is placed.Based on this method,the combined lens is designed for rectangular illumination.The result shows the performance of the target plane meets the requirements of rectangular lighting.The uniformity is about 88% and the lighting efficiency is improved to 75%.Based on the design idea of the combined lens,considering that the diffuse reflection surface is obtained by lofting of two boundary curves,the diffuse reflection surface has not been specifically designed,and the lighting effect produced by this diffuse reflection surface has limitations.In order to further improve the lighting effect of the target plane,the design of the double freeform surface lens is carried out.The lens contains a refractive freeform surface and a diffuse freeform surface.Different from the universal double freeform surface lens,this double freeform surface lens is divided into a small-angle freeform surface and a large-angle diffuse reflection freeform surface.The small-angle freeform surface firstly limits and forms the lighting area.Then,the large-angle freeform surface is designed to improve the efficiency of lighting area.And this front light diffuse reflection effectively avoids the influence of light source projection onto the lighting effects.Based on this design method,the double freeform surface lens is obtained.The results shows the efficiency of a circular lighting area reaches 81% and the uniformity of the irradiance distribution reaches 91%.And this design is also suiTab.for forming different shapes of lighting areas while maintaining a better lighting effect.