Design of microstructure optical film for high uniform mini-LED backlight

In recent years, Mini-LED has been widely used in direct-lit backlight for Liquid Crystal Display (LCD) widely due to its advantages of miniaturization and low power consumption. Typical Mini-LED direct-lit backlights mainly rely on the diffuser plate to convert point-like light sources into uniform surface light sources. However, the diffuser plate cannot achieve high uniformity at a very low optical distance (OD). In this paper, we introduced the pyramidal microstructure and the semi-cylindrical microstructure to both sides of the optical film, respectively. The mechanism of influence of the pyramidal microstructure and the semi-cylindrical microstructure on light was analyzed. We clarified the relationship between the parameters of the microstructure (the pyramid angle, the pyramid dimension) and the illuminance uniformity by simulation. Moreover, two layers of microstructure optical films are discussed and simulated. Through the simulation, the optical effects are evaluated and analyzed from the point of illuminance uniformity. Simulation results maintain that when the OD is 5mm, the illuminance uniformity reaches 93.07%. Compared with the diffuser plate with a thickness of 1.5mm, the thickness is reduced by 0.9mm, and the illuminance uniformity is increased by 11.77%. This work fully demonstrates the advantages of the microstructure optical film to improve the illuminance uniformity.