Design And Application Of Freeform Fresnel Surface TIR Lens

As an emerging lighting source,LED has the advantages of high photoelectric conversion efficiency,low power consumption,long life,small size and environmentally friendly compared with traditional light sources.Urbanized road illumination based on LED light sources has become an important part of current research.When the LED is applied to road lighting,it is necessary to perform secondary light distribution design for the LED light source.The secondary light distribution lens currently used for road illumination is mainly a TIR(total internal reflection)lens.This lens has a problem of a large size and poor heat dissipation.In this paper,the Fresnel surface is superimposed on the TIR lens with the freeform surface on the exit surface,and the lens with thinner thickness and lighter weight than the traditional free-form TIR lens is designed.The design is extended accordingly.The main research contents are as follows:Firstly,according to the light source parameters and the design requirements of the road illumination,the data of TIR double freeform surface is obtained by applying the law of conservation of energy,edge ray theory and Snell's law;in order to simplify the manufacturing process and reduce the cost,the data of the TIR single freeform surface is obtained.Then,exit surface of the single free-form surface TIR lens is constructed to the Fresnel surface and optimized to obtain the freeform Fresnel surface TIR lens.The illuminance uniformity and light efficiency of the three TIR lenses are analyzed.Tolerance analysis was performed on the TIR lens with Fresnel surface.Finally,the illumination array design and a near-field projection illumination system design and optimization were completed with a freeform Fresnel surface TIR lens.The simulation results show that the illuminance uniformity of the three optimized freeform surface TIR lenses is 83.3%,82.0%and 82.0%,and the light efficiency is 98.2%,98.2%and 96.6%,indicating the TIR lens still maintains a good illumination effect after Fresnelization of the freeform surface.In terms of shape and volume,the height of the exit freeform surface of TIR lens after Fresnelization is reduced from 8.6mm to 1.08mm,while the volume and mass are also reduced by about 20%,which makes the optical path of the LED light inside the lens greatly shortened,effectively improving the heat dissipation efficiency and service life of the lens.Tolerance analysis shows that,Under the relatively loose tolerance setting,the maximum lighting loss caused by the position error of single light source is not more than 3.2%,which has little influence on lighting.From the application of Fresnel surface TIR lens,a good array design can increase the illumination value of far-field illumination exponentially without reducing the light efficiency.When used alone in near-field projection illumination,the illumination uniformity reached 78.3%and the light efficiency reached 94.3%.When combined with compound eye lens and focusing lens,the illumination uniformity and the light efficiency both increased by 4%.