Compact freeform primary lens design based on extended Lambertian sources for liquid crystal display direct-backlight applications

A concept for a freeform primary lens system (FPLS) is proposed for designing freeform optics in the direct-backlight system of liquid crystal displays. This FPLS has a super small ratio of height of the optics system h to LED source with diameter D by avoiding the use of traditional secondary optics for LED illumination applications. The FPLS is first designed based on energy conservation principles and ray mapping techniques, and improved through feedback optimization algorithms. Both simulation data and experimental data are employed successively to improve the illumination uniformity on the target plane. Meanwhile, the divergence angle of the FPLS is further improved to achieve a more uniform irradiance distribution pattern of the LED luminaire array on the target plane with an ultrashort projection distance between source and target. We demonstrate the concept by designing and manufacturing an FPLS; the experimental data show that, with h/D = 0.98 of the optical system, the relative standard deviation of the target area reaches 0.22 within the divergence angle of 120 deg. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)