Design Of Double Freeform Surface Lens For Direct-Lit LED Backlight Unit

LCD has become the mainstream flat panel display,which presents a wide application in all aspects of people's production and life.As a key component of a liquid crystal display,backlight unit is gradually developing toward the direction of large size,ultra-thin and low cost.To reduce the mixing distance,secondary lens are employed to redistribute the light of LED light sources,which makes the design of the lens become very important.Based on the theory of non-image optics,a design method of double freeform surface lens in LED backlight unit is proposed in this thesis.Firstly,the optimal illumination distribution on the target surface of the single lens is discussed and determined.Then,the initial surface design method based on the optimal illumination distribution on the target surface is proposed.The first optimization design based on illumination feedback is carried out and the second optimization design based on the overlap method is used for the second optimization of the lens surface.Two kinds of lens with the mixing distance of 22 mm and 10mm(OD22mm and OD10mm)are designed by the above method.The simulation results show that the illumination uniformity of the bakclight unit with the OD22 mm lens and OD10 mm lens is 91.00% and 94.76%,respectively.The actual OD22 mm lens is manufactured and tested.The test results show that: after using the designed double freeform surface lens,the 9 point uniformity of the backlight unit reach 87.98%.The double surface freeform lens designed in this thesis can effectively satisfy the design requirement of array uniformity without increasing the thickness of backlight unit,which can help develop ultra-thin backlight unit.