ABSTRACT
We analyze the performance of high dynamic range liquid crystal displays (LCDs) using a two-dimensional local dimming mini-LED backlight. The halo effect of such a HDR display system is investigated by both numerical simulation and human visual perception experiment. The halo effect is mainly governed by two factors: intrinsic LCD contrast ratio (CR) and dimming zone number. Based on our results, to suppress the halo effect to indistinguishable level, a LCD with CR≈5000:1 requires about 200 local dimming zones, while for a LCD with CR≈2000:1 the required dimming zone number is over 3000. Our model provides useful guidelines to optimize the mini-LED backlit LCDs for achieving dynamic contrast ratio comparable to organic LED displays.
ABSTRACT
We develop a rigorous model to simulate an LCD's contrast ratio (CR) and viewing angle by considering the depolarization effect in thin-film transistor substrate, LC layer, color filter (CF) array, etc. To mitigate the depolarization effect, we propose a new device structure by adding a thin in-cell polarizer between LC layer and CF array. Based on the analysis using our new model, the maximum CR of a multi-domain vertical alignment (MVA) LCD can reach > 20,000:1, while for the fringe-field switching (FFS) mode it can reach > 3000:1. We also discuss other approaches to further enhance the CR. Our model is a powerful tool to analyze the CR degradation mechanism and to guide the future LCD device and material optimizations.
ABSTRACT
We report a vertically-aligned liquid crystal display (LCD) device with submillisecond response time, high transmittance, and low operation voltage. The top substrate has a common electrode, while the bottom substrate consists of hole-patterned fringing-field-switching (FFS) pixel electrodes. A negative dielectric anisotropy LC is employed. In the voltage-on state, the LC directors are reoriented by the fringing fields surrounding the hole area and by the longitudinal and fringe fields outside the hole area. After design optimization, we are able to achieve 85% peak transmittance under crossed circular polarizers. During the relaxation process, the standing walls exert a strong restoring force, leading to submillisecond gray-to-gray response time. Moreover, this device enables high resolution density because only one thin-film transistor per pixel is needed and the bottom FFS electrode has built-in capacitor. This device is particularly attractive for the emerging virtual reality displays.
ABSTRACT
We propose to add a functional reflective polarizer (FRP) in the backlight unit to suppress the crosstalk between red, green and blue color filters of a liquid crystal display (LCD) panel. When incorporated with a commercial two-phosphor-converted white light-emitting diode (2pc-WLED), the color gamut of the LCD can be improved from 92% to 115% NTSC standard, which is comparable to the cadmium-based quantum dot (QD) backlight. If a narrow-band color filter is employed, the color gamut can be further enhanced to 135% NTSC. Our design offers an alternative approach to QDs, while keeping low cost and long lifetime. Such a simple yet efficient approach would find widespread applications for enlarging the color gamut of LCDs.
ABSTRACT
We propose a high dynamic range (HDR) liquid crystal display (LCD) with pixel-level local dimming. The device structure consists of a pixelated LCD dimming panel to control the backlight intensity entering the master LCD panel. According to our analysis and test cell experiment, this dual-panel display system possesses exceedingly high contrast ratio (> 1,000,000:1) and high bit-depth (> 14 bits) at merely 5 volts. Meanwhile, to mitigate the Moiré effect induced by the cascaded thin-film transistor (TFT) backplanes, we separate the two LCD panels with a polarization-dependent scattering film. The pros and cons of this HDR display are discussed.
ABSTRACT
In this study, we analyze how a backlight's peak wavelength, full-width at half-maximum (FWHM), and color filters affect the color gamut of a liquid crystal display (LCD) device and establish a theoretical limit, even if the FWHM approaches 1 nm. To overcome this limit, we propose a new backlight system incorporating a functional reflective polarizer and a patterned half-wave plate to decouple the polarization states of the blue light and the green/red lights. As a result, the crosstalk between three primary colors is greatly suppressed, and the color gamut is significantly widened. In the experiment, we prepare a white-light source using a blue light-emitting diode (LED) to pump green perovskite polymer film and red quantum dots and demonstrate an exceedingly large color gamut (95.8% Rec. 2020 in Commission internationale de l'éclairage (CIE) 1931 color space and 97.3% Rec. 2020 in CIE 1976 color space) with commercial high-efficiency color filters. These results are beyond the color gamut limit achievable by a conventional LCD. Our design works equally well for other light sources, such as a 2-phosphor-converted white LED.
ABSTRACT
We propose a versatile design approach of engineered diffuser based on freeform optics that can tailor the light distribution of a liquid crystal display (LCD) to meet different applications. The proposed LCD system consists of a quasi-directional backlight, liquid crystal panel, and an engineered diffuser. It offers high efficiency, wide view, high contrast, as well as low ambient light reflection. For large size LCDs, we design a wide view diffuser to match the light distribution with state-of-the-art organic light emitting diode (OLED) TV. For mobile displays, we design a diffuser to replicate current LCD performance. Our design can also provide flattop light intensity distribution for privacy protection. These exemplary designs prove that our engineered diffuser is versatile for different applications.
