Design And Optimization Of Several Freeform Surfaces In Nonimaging Optics

Light-emitting diode(LED)has the advantages of high luminous efficacy,long life,and small size.Correspondingly,LEDs are gradually replacing the conventional lamps and widely used in indoor and outdoor lighting.However,direct application of LED light source has the shortcoming such as poor lighting efficiency,light pollution and waste of light,and it is also difficult to meet the requirements of practical lighting in different application occasions.Hence,optical design is required to regulate light ray of the LEDs.In the nonimaging optical lighting design,the optical system based on freeform surface is one of the hot spots due to its high design freedom and flexibility.In the design of an ideal optical system,the light source is usually regarded as an ideal point.However,the size of the real light source cannot be neglected in practical application.When the optical system is compacted in a certain degree,the light source cannot be treated as a point.In this paper,nonimaging optical theory,freeform surface modeling,optimal design and optimal transport theory are combined to design freeform lens based on the extended light source to realize uniform circular light distribution,circular light distribution and square light distribution.First,freeform surface lens is design to realize circular uniform illuminance distribution.A cumulative feedback optimization algorithm based on illumination deviation restrained by energy mapping relationship and easy processability is proposed.In this optimization algorithm,a chip-on-board(COB)LED with a large light emitting surface and non-uniform brightness is used as a light source and the processing feasibility of the optical device is taken into consideration.Based on the proposed optimization algorithm,a freeform surface lens with a Cree's CXA1816 COB LED light source is designed.The results show that a circular uniform illumination light distribution with the relative standard deviation(RSD)of 0.0062 is achieved in a circular region with a radius of 1480 mm and a distance of 1000 mm from light source.The RSD still remains a low value of 0.0801 in the circular region with a radius of 1730 mm.Second,freeform surface lens is designed to realize ring uniform illuminance distribution.A design method of freeform surface lens based on the multi-parameter optimization of Bezier curve control points is proposed.The algorithm based on the point source is used to design the freeform surface lens profile,and Bezier curve fitting is used to construct the initial model before optimization.The optimization algorithm is used to adjust the Bezier curve control point to obtain the optimal freeform surface model.The results show that a ring uniform illumination light distribution with an outer radius of 2000 mm and an inner radius of 1000 mm is achieved in the target plane at a distance of 1000 mm from the light source.The uniformity of illumination distribution is 0.91 and the light control efficiency reaches 0.80.Third,freeform surface lens is designed to realize the square uniform illuminance distribution.Combining the optimal transport theory and optimized design method,a freeform surface lens design method suitable for the extended light source is proposed.Using this algorithm,a freeform surface lens with uniform square light distribution is designed.In the design process,the optimal transport theory is used to design the initial lens model based on the point source,and then the inner freeform surface of the lens and the position of the light source are optimized.Based on the results obtained from the first optimizing step,combined with the feedback optimization algorithm,the outer freeform surface is optimized and a freeform lens model based on the LED extended light source is designed.The results show the square uniform illuminance distribution with a side length of 1996 mm is achieved in the target plane 1000 mm away from the light source.In the square region,the illuminance uniformity in the target plane is 0.046 and the light control efficiency reaches 0.80.