Designing Freeform Micro Lens Array With Prescribed Luminous Intensity for LCD Backlight Units

The precise luminous intensity control for liquid crystal display (LCD) backlight units is an important issue that has not been well addressed in current research. A proper luminous intensity distribution can significantly enhance the viewing experience. In this paper, we propose a method for designing a freeform micro lens array that is capable of producing a prescribed luminous intensity distribution for direct-lit LED backlight module. As the luminous intensity distribution is usually need to be constrained within a quadrilateral pyramid region, a special coordinate system is developed by scanning two semicircles containing light rays along the X axis and Y axis to provide a flexible model for luminous intensity tailoring. Further, we convert the luminous intensity design problem to a specific illuminance problem by using a lossless energy conversion strategy. Then, an integrable ray mapping between the source domain and the target domain is established to implement the freeform optics design to regulate the converted illuminance distribution. The effectiveness of the proposed method is verified via various design examples including on-axis configuration and axis-off configuration, the influence of the LED size on the optical performance is also analyzed.