Lens film design and preparation for LC image source in helmet display

LED has become a mainstream light source in helmet liquid crystal (LC) display. To increase luminance and decrease backlight unit volume, a flatening design of double free-form surface lens was carried out to form the lens film. The simulation results show that the central luminance increases and the spot size decreases after lights passing through the lens film. The feedback optimization was performed to redefine the power distribution when designing the double free-form surface lens, and the lens film is redesigned. The simulation results illustrate that the spot size increases from 2.3 mm to 7.1 mm after optimization. The designed lens films were prepared by maskless direct-writing lithography, and each film contained a free-form surface. The backlight units with and without the lens films were measured, and the measured results show that the average luminance with the lens film increases by 18.1%. The designed lens film can effectively increase the luminance and decrease the backlight units volume.