Dimming Technology Research Articles

Mini-LED Backlight: Advances and Future Perspectives

Miniaturized-light-emitting diode (mini-LED) backlights have emerged as the state-of-the-art technology for liquid crystal display (LCD), facilitating the improvement in a high dynamic range (HDR) and power saving. The local dimming technology divides the backlight into several dimming zones. Employing mini-LEDs, whose size ranges from 100 to 200 μm, as the light sources can enlarge the number of zones in the local dimming backlight, fulfilling the requirement for HDR. However, the halo effect still acts as one of the primary technological bottlenecks for mini-LED backlights. In this review, packaging technology of LEDs, color conversion, and the driving scheme of mini-LED backlights have been discussed. The strategies to reduce optical crosstalk in adjacent areas by various improved optical structures or to suppress the halo effect of LCDs by mini-LED backlights are summarized. The development trends of mini-LED backlights are also discussed.

79‐1: Invited Paper: Adaptive Local Backlight Dimming Control with Local Boosting

The local backlight dimming (LBD) technology has attracted significant interest for liquid crystal displays. In automotive, notebook PC, and virtual reality applications, LBD should treat the trade‐off between power saving and visual quality enhancement. However, it requires the cost of the high logic complexity to consider the optimal solution at a higher resolution of the image. This paper proposes the adaptive local backlight dimming control, which can reduce the power consumption of backlight and improve the quality of the display. The proposed method analyzes an image contents with a low complexity algorithm, and it applies a local boosting to achieve a target intensity in backlight control. In performance evaluation using FPGA test system, the designed local dimming processor achieved 7.54% higher power‐saving rate with visual quality enhancement in high‐contrast region.

79‐2: Peripheral Dimming Technique Depending on Field‐of‐View for Low‐Power Head‐Mounted Devices

We have proposed peripheral dimming technology that reduces the image brightness in peripheral area based on the human visual system. This study presents how peripheral dimming should be applied depending on the screen field of view (FoV) the user watches. Threshold conditions for peripheral dimming of various FoVs are derived through user study in an environment simulating virtual reality.

Study on polymer dispersed liquid crystal films with wide viewing angle

ABSTRACT Polymer Dispersed Liquid Crystal (PDLC) films have been widely used as electronically controlled dimming technology, and solving the problem of narrow angle of PDLC is a cutting-edge challenge for their application. In this paper, a theoretical model of the viewing angle characteristics of PDLC is constructed, and the corresponding samples are experimentally fabricated. It is found that the simulation results of transmittance changing with the viewing angle are in good agreement with the experimental results. Furthermore, the technical approaches to improve PDLC viewing angle characteristics and achieve a wide viewing angle are discussed theoretically. The results show that the PDLC films for wide viewing angle can be obtained by using liquid crystal materials with smaller anisotropy of refractive index and polymer materials with refractive index slightly higher than the ordinary refractive index of liquid crystal.

Adjustable High-Power Light Emitting Diode Driving Circuit and Its Lighting Application in Sports Venues

High-power LED not only has the characteristics of energy saving, environmental protection, long service life, and high reliability, but also has the advantages of high light efficiency and large conduction current. According to the characteristics of high-power LED, an adjustable high-power LED driving circuit is designed in this study. The chip adopts the Boost circuit structure driven by constant current, and the output current on a single channel is converted into voltage by using the sampling resistor on the LED path and fed back to the circuit. After passing a mirror current independent of temperature through a resistor, the reference voltage source is obtained by voltage division. When designing the LDO circuit of voltage regulator, modules such as front-end voltage conversion circuit and input under voltage protection circuit are added. When designing the soft start circuit, the output voltage of the soft start replaces the output of the error amplifier and is connected to one end of the PWM comparator. In the design of dimming circuit, PWM dimming technology is adopted, and the DIM pin is connected to low level when there is no PWM signal. In the experiment, the lowest level of soft start is 0.78 V, the highest bit is 1.35 V, and the period is 374.6 us. When VIN = 8 V, the output voltage can be adjusted to 40 V in one period based on soft start, which meets the starting requirements of the driving circuit. When the DIM pin is connected with a PWM dimming signal with a duty ratio of 90% and a frequency of 10 kHz, the output current of the LED light is in a relatively stable state. Applying the designed LED driving circuit to the lighting of sports venues can meet the requirements of daily events and training, and has advantages in energy saving and environmental protection.

Reverse polarity optical Orthogonal frequency Division Multiplexing for High-Speed visible light communications system

The radio frequency spectrum, which has been steadily getting smaller, is under pressure from growing cellular data traffic. A more dependable communication channel is required. To setup the communication medium, VLC uses LED illumination. In order to increase network throughput, the goal of this study is to analyze and model signal conditioning techniques in the visible spectrum. VLC technology offers synchronized illumination of LED lamps as well as wireless broadband connectivity. Using the real-valued O-OFDM baseband signal, optical orthogonal frequency division multiplexing (O-OFDM) offers a viable modulation option for very-low-bit-rate (VLC) systems to modulate the optical carrier's instantaneous power to attain gigabit data rates. However, one important design difficulty preventing VLC from being commercialized is how to combine industry-favored pulse width modulation (PWM) dimming technology while retaining a dependable, broadband connection. In this paper, Reverse Polarity optical orthogonal frequency division multiplexing (RPO-OFDM) is proposed as a new signal format for combining the fast O-OFDM contact signal with the comparatively slow PWM dimming signal, as both signals contribute to the illuminative brightness of the LED. The average SNR, additional testing demonstrates that the suggested method outperforms the Asymmetrically clipped optical OFDM (ACO), Optimized Flipped Optical (OFO) and DC biased optical OFDM (DCO), and algorithms in similar operating conditions.

P‐49: Picture Quality Evaluation Method on LCD with Local Dimming Technology †

In this paper, a novel objective evaluation method is proposed to quantify the picture quality. In particular, the effect of “halo” and ‍“backlight delay” is taken into consideration in the design of the evaluation pipeline. The objective evaluation method is used to test ‍the picture quality, and the results are compared with the subjective ones, demonstrating the effectiveness of our proposed evaluation ‍method.

34‐3: Research on Vehicle mounted Projection Display with Local Dimming Effect

With the development trend of large on‐board screen and intelligent driving, PHUD, as a new type of car head up display application scenario, has gradually attracted the attention of various automobile manufacturers. It greatly simplifies the system design by highlighting modules, specific angle of view steering design, and one‐time windshield projection. At the same time, it carries BD cell Local Dimming technology to achieve exquisite HDR projection display and greatly reduce module drive power consumption, and the contrast can reach millions. This paper mainly studies a module display combining BD cell local dimming and PHUD technology.

Minimization of halo mura in homogenous alignment liquid crystal displays via a dichroic light absorber [Invited

Local dimming technology enables high dynamic range liquid crystal displays (LCDs). However, when displaying a bright image in a dark background, so-called halo mura (halation caused by local light leakage in oblique viewing directions) appears and degrades image quality owing to reduction in contrast ratio (CR). Here light-absorbing vertically aligned dichroic dye film cells are demonstrated to enhance the CR in a homogenously aligned LC mode. The light leakage in normal and oblique viewing directions is reduced greatly in both simulated and experimental results. Positioning such a functional film above the conventional polarizer can greatly improve the CR of all LCDs while reducing surface reflection.

P‐17.1: Research on Halo Effect in Mini LED Backlight

In recent years, with the improvement of consumers' pursuit of display quality, in the field of LCD display, the direct‐light backlight technology is increasingly used in TV, MNT, NB, VR, Pad and even automotive display fields. Using this technology to zone the backlight can achieve local dimming technology, that is, adjust the brightness of the single backlight zone according to the image. Thus, high contrast ratio and high color gamut can be achieved while reducing power consumption. However, compared with the traditional edge‐light display, the halo effect of the direct‐light backlight display greatly affects the visual effect. At present, backlight design tends to be highly zoned, which will affect the halo effect and contrast ratio. And as customers pursue further improvement in optical property, the 3D reflector design to enhance the luminance of the single zone will also affect contrast ratio and halo effect. In this paper, we explored the influence of zone size and 3D reflector design on halo effect and contrast ratio, so as to guide the subsequent products to carry out appropriate zone size design.

49.1: Visual Quality System ‐ A Simulation Solution for Mini‐LED LCD Backlight Unit Optimization Targeting on High Quality and Accurate HDR Image Display

Local dimming technology has largely increased the effective contrast ratio of mini-LED displays. With suitable backlight and algorithm design, these devices are capable of rendering HDR images with extreme quality. A solution for mini-LED backlight optimization is presented in this work. VQS utilizes deterministic light propagation simulation and spectral analysis to predict display quality from design parameters. It provides display system manufacturers and local dimming algorithm developers a framework to easily optimize their designs.

P‐6.2: Picture Quality Evaluation Method on LCD with Local Dimming Technology

In this paper, a novel objective evaluation method is proposed to quantify the picture quality. In particular, the effect of “halo” and “backlight delay” is taken into consideration in the design of the evaluation pipeline. The objective evaluation method is used to test the picture quality, and the results are compared with the subjective ones, demonstrating the effectiveness of our proposed evaluation method.

P‐35: The Study of Vehicle Bright Backlight with Local Dimming Effect

Using Local Dimming technology, the LED backlight can be adjusted according to the image of the light and shade, the brightness of the display image's highlight part can reach the maximum, at the same time, the dark part can reduce brightness, or even shut down, in order to achieve the best contrast ratio. Meanwhile, as a new type of car visual interactive equipment, AR‐HUD (head‐up display) is developing rapidly in recent years, according to statistics, more and more car owners choose to install AR‐HUD equipment in their cars.This paper mainly studies on a highlight backlight which combines the Local Dimming and AR‐HUD technology.

64‐1: Local Dimming Technology of Scene‐Adaptation for Massive Mini‐LED

Mini‐LED Backlight Units can reduce the light mixing distance and the number of backlight blocks, making the monitors lighter and thinner, achieving higher contrast and better effects. As a leading company in the panel display industry, BOE has been developing Mini‐LED technology since 2016, and has developed 65', 75', and 86' smart commercial display monitors based on Mini‐LED technology.This paper verifies the Local Dimming technology with multiple partitions using FPGA, it's safe to say that it obtains a finer light distribution and less halo effect, which will strongly support MiniLED display products in the future.

Pengaruh Sistem Peredupan terhadap Efisiensi Energi Penerangan Jalan Umum pada Universitas Indonesia Berdasarkan Metode Lumen

LEDs in lighting systems have been widely used, including public street lighting systems. However, the selection of public street lights in Indonesia often does not use lumen calculations and light dimming technology. This study aims to improve energy consumption efficiency by replacing existing lamps with LED lamps according to the lumen calculation method and using a smart system in the form of automatic dimming of the lamps. The research study was carried out in two stages: the measurement of illumination using a lux meter and the analysis of energy consumption between the existing and the replacement. The replacement scenario is to replace the existing lamps with LED lamps equipped with an automatic dimming system based on lumen calculations. The lighting level is adjusted to Indonesian lighting standards, SNI 7391:2008, 2 to 5 lux. The result of the study is that carrying out a replacement scenario can increase energy consumption efficiency by 77.95%.

Intelligent Street Light Control System Based on Fuzzy Control Algorithm

In view of the low efficiency and intelligence of street lamps in the city street and the high proportion of manual monitoring, we designed an intelligent street lamp system. The street lamp system consists of hardware part and software part. The hardware part takes STM32F103ZET6 single chip microcomputer as the microcontroller of the main control system, the signal acquisition of the light sensor through I2C bus, and uses PWM dimming technology to adjust the brightness of LED lamp. The software part mainly uses the fuzzy control algorithm to achieve the intelligent control of street lamps includes the designed lighting fuzzy controller and vehicle speed fuzzy controller. The algorithm is simulated and analyzed by using MATLAB, and the algorithm is combined with the hardware system for experimental test. The simulation analysis and test show that the system can simulate of manual control process and method intelligently, which provides a reference for the current use of street lamp lighting in conventional sections.

12.3: Research on Reducing H: P Value of Lensless Direct‐lit Backlight Module

The direct‐lit mini LED backlight LCD module can utilize ultra‐fine local dimming technology. This approach can realize not only the thinning of backlight unit, but also more refined dynamic control, improving the dynamic contrast of liquid crystal display. As displays continue to develop toward thinness, the number of required LED chips has increased significantly, causing cost and energy consumption issues. The industry usually uses H: P value (OD/LED pitch) to describe the relationship between the cost and thickness of the backlight module. In this work, mini LED technology was researched and applied. Firstly, a blue light angular bidirectional optical film was applied. By controlling the thickness and refractive index of the multilayer film, an effect of reflecting a small angle and transmitting a large angle of blue light was realized, which increased the irradiation range of a single LED. In this way, the H: P value can be reduced from 0.6 to 0.3. Then top shielding structure of the secondary package was used to expand the light‐emitting angle of the mini LED chips, which reduced the H: P value from 0.64 to 0.48. Finally, the two schemes were combined to bring the H: P value to 0.24. This design reduced the thickness of the module under low‐cost conditions and reached the most advanced level in the industry.

Deep CNN-based local dimming technology

Deep CNN-based local dimming technology

P‐152: A High Precision and High Contrast Algorithm based on Dual‐cell LCDs

Local dimming technology can significantly improve the contrast ratio (CR) of LCD products, the more the backlight units, the higher the CR. But due to technical limitations, backlight partitions cannot be made particularly fine. By adding a layer of light control cell between backlight and display panel, the pixel‐level local dimming can be achieved. This paper proposed a high precision and high contrast algorithm based on dual‐cell LCD. The proposed method took pixel shape and position into account which can guarantee two cells matching perfectly and realize low distortion and high contrast display.

A Stronger Aadaptive Local Dimming Method with Details Preservation

Local dimming technology focuses on improving the contrast ratio of the displayed images for a great visual perception. It consists of backlight extraction and pixel compensation. Considering a single existing backlight extraction algorithm can hardly adapt to images with diverse characteristics and rich details, we propose a stronger adaptive local dimming method with details preservation in this paper. This method, combining the advantages of some existing methods and introducing the combination of the subjective evaluation and the objective evaluation, obtains a stronger adaptation compared with others. Besides, to offset the luminance reduction caused in the backlight extraction process, we improve the bi-histogram equalization algorithm and propose a new pixel compensation method. To preserve image details, the Retinex theory is adopted to separate details. Experimental results demonstrate the effect of the proposed method on contrast ratio improvement and details preservation.