Design And Optimization Of Large-size Direct-type LED LCD Backlight System

LED backlight has become the mainstream of LCD-TV, comparing with direct-typebacklight system, edge-type backlight system using in the large-size LED LCD owning lowoverall brightness, uniformity and contrast. Large-size direct-type LED backlight technologyis not yet very mature, and how to solve ultra-thin design of direct-type LED backlight systemhas become is quite crucial. Therefore, it is great significant to study the design method, andwe mainly focus on two different design methods for direct-type LED backlight system in thispaper.Two different design methods for direct-type backlight system have been proposed: forlow-power white LED direct-type backlight system, we analyze and calculate the theoreticalmodel of LED illumination distribution in the near-field illumination surface and propose thestructure using interlaced non-uniform arrangement, and get the relationship of LEDhorizontal spacing distance, vertical spacing distance, backlight module mixing height duringthe non-uniform arrangement by theoretical calculation, and calculate the maximally-flatconditions to meet the uniformity of backlight system, achieving rapid and effective design inlow-power LED direct-type backlight system. For high-power white LED direct-typebacklight system, we propose one kind of structure using optical divergent lens combinationwith LED, and design the uniform square spot lens in the ultra-shot space distance based onnon-imaging theory. Taken the target illumination surface dividing into numbers of uniformrectangular grids, then divide the angle of LED source proportionally and make therectangular grids of target illumination surface and the angle of LED source for one-to-onecorrespondence, obtaining corresponded energy relationship. Then we get the curvilinearcoordinate values of free-form lens by calculating the vector expression of Snell’s law andfinally get the lens models through cure interpolation fitting.For the purpose of practical verification of design methods in the paper, we produce andtest46-inch low-power LED direct-type backlight and55-inch high-power LED direct-typebacklight sample. Test results show that the design methods proposed in the paper havecertain practical value.