Optical Study And Improvement Of Back Light Unit For Liquid Crystal Display

Backlight,as a critical optical component of LCD is thinner,narrower,lighter,brighter,and low-power which has become the main trend.Focusing on the main problems of backlight brightness and uniformity,this thesis starts with the analysis of the backlight structure and conducts research and discussion on the materials afifecting its optical parameters.And optical defects can be eliminated by controlling the quality of secondary materials.The main results are as follows:(1)LED improves the optical brightness by selecting LED with larger scale of light or using polycrystal LED design to improve the brightness by increasing their own luminous quantity.At the same time,increasing the driving current can directly increase the brightness of the LED,but the maximum current can't exceed the tolerance range of the bracket plastic.Secondly,the phosphor with the best brightness performance is preferred under the same input power and the same color temperature.At the same time,it is necessary to consider the heat resistance of different phosphors,and the phosphor with better heat resistance has better balance light efficiency.Once the LED light source is determined,the utilization rate of the LED light and the final brightness of the backlight unit can also be improved through adjusting the mechanical design,including adjustment of the rubber strip's thickness,additional convex strip design of the rubber frame structure,and blackening of the diaphragm to prevent the light leakage through the gap.At the same time.LED-LGP(light guide plate)coupling distance determines the luminous efficiency as well as the luminous uniformity.The gap of 0.2mm is used as the design starting point,which can effectively avoid the waste of luminous energy.(2)LGP diverts light out of the light surface through network dots.Different arrangement of the network dots have different utilization rate of light energy and regional brightness can be increased with higher-density network dots.Since the light intensity is decreasing from the LED side to the light-emitting side,the dots network is designed with its density increasing from light bar side to the other side.It is also found,in the printing process of LGP,that scraper speed,returning ink knife speed,scraper printing angle and ink viscosity have great influences on the size and roundness control of the network dot.(3))During the assembly process,the LED-LGP gap affects the utilization of light energy.With the larger gap,the less light of LED enters LGP.However,LGP can be thermally melted by LED heating if LGP gets too close to the light bar.So the gap is finally optimized 0.5 mm and limit jig auxiliary is used for assembly work to avoid operating defect.The above research provides a relatively complete solution for backlight optic and size design which effectively prevents repeated verification work and mass cost loss.