Correlation between the gain factor of a reflective polarizer and the optical structure of quantum dot-based backlights for LCD applications

The optical gain factor of a reflective polarizer in a quantum dot (QD)-based edge-lit backlight was investigated for the first time with various optical film combinations. The QD film, containing red and green quantum dots, was excited by 20 blue LEDs arranged near the light guide plate (LGP). The multilayer-type reflective polarizer significantly altered the color properties of the QD backlight by enhancing QD film excitation through its reflective properties. The gain factor was nearly two when only a single QD film was placed over the LGP without additional optical films, indicating minimal optical loss. However, the gain factor decreased significantly with the addition of prism sheets, likely due to the formation of a strong optical cavity between the bottom reflector and the prism grooves. This suggests that the optical configuration of QD-based backlights should be carefully optimized to account for color changes due to the reflective polarizer and to avoid strong optical cavity effects caused by prism sheets.