LED Backlight System Research Articles

Direct Design of Thin and High-Quality Direct-Lit LED Backlight Systems

The direct-lit LED backlight is a key component in large-area LCD displays. The existing methods which rely on point source assumption and irradiance feedback are less effective in compact designs in near field, and designing thin and high-quality back-lit LED backlights still remains a challenging issue. In this paper, we develop a direct method for designing thin and high-quality back-lit LED backlight systems. The étendue of LED light sources is considered in the numerical calculation of the lens profiles without cumbersome Monte Carlo ray tracing, which allows us to obtain compact LED lighting modules and achieve accurate control of the near-field irradiance distribution of the backlight system. Two examples are presented to demonstrate the elegance of this method in designing thin and high-quality back-lit LED backlights.

Lighting assessment of ergonomic workstation for radio diagnostic reporting

Within the diagnostic process, in the activities in which digital radiology systems are utilised, image display devices play a very important role. Such devices have to guarantee high performances in order to maintain the diagnostic quality of the displayed images and present them so that they can be observed optimally. In order to ensure the appropriate performance to the users, not only the image display device but also the whole workstation should be designed properly. Particular attention should be paid to the lighting conditions, to avoid compromising the radiologist's ability to observe the displayed images.The aim of this study is to assess the lighting of some workstations used for diagnostic radiology reporting, in order to obtain information about the visual interaction between worker and device and prevent health risks. A detailed analysis of the lighting of adjustable and nonadjustable workstations used for diagnostic radiology reporting was carried out in different rooms of the Radiology Department at the “Felice Lotti” Hospital in Pontedera (Pisa, Italy). The analysis was carried out thanks to in situ measurements (objective analysis) and the submission of an evaluation questionnaire to a sample composed by 16 radiologists (subjective analysis).From the obtained results it has been possible to point out that, in nonadjustable workstations the absence of a dedicated lighting system very often reveals the inadequacy of the general lighting in guaranteeing correct lighting conditions for the radiologists during the reading of the diagnostic monitors. As measure to reduce the visual fatigue of the radiologists, the use of a supplementary adjustable innovative LED backlight system was proposed. The use of the LED backlight system allows complying the requirements of the Technical Standards and mitigate the difference of luminance in the field of view of the radiologist. Due to that the use of the LED backlight system has been positively perceived by the examined sample, a significant part of whom has ascribed to this use a reduction in the visual fatigue.

Intratubal optical defectoscopy of working chimneys

In this work we consider methods to improve the quality of defectoscopy in a chimney using a stand-alone unit (SU) with camcorders, which is sent down a chimney, where the camcorders make serial photographs of the parts of the surface. The SU allows one to detect defects with a size of 2 mm. It oscillates when it is moving in the opposite direction in the upward flue gas stream. The periodic tilting of the camcorders causes the periodic displacement of the shooting directions and the camera movements lead to the effect of blurred images. A cyclic mode that uses incandescent bulbs causes a loss of energy in each cycle due to their pre-heating. The problem of improving the resolution of the intratubal chimney control by equipping the SU with gyro-stabilized platform for video cameras and a power-saving LED backlight system was solved.

RGB Primary Color LED Backlight System Based on MCU

A solution was proposed for the purpose of backlight. According to the principle of three primary color£¬A kind of RGB led backlight was designed with ncp6223 chip dedicated to the RGB illumination or backlight LCD display when ncp5623 was controlled by MCU. The realization of I2C bus which was used to control ncp5623 was taken the measure of direct driving of ncp5623 Using two arbitrary general-purpose IO pin of MCU. In respect of communication protocol, the software simulation was taken. Moreover only minimum system was needed for MCU. This method mentioned above simplified design and cut the cost because of absence of master I2C controller. In respect of software design, every template which realized a function of ncp5623 in the manner of software simulation of I2c protocol was given. In another word, a general method was given. From these templates, a lot of design such as Gradual intensity Dimming, RGB function and so on can be realized. This has a great signification for teaching and practice.

59.2: A Novel LED‐Backlight System with Tilted Cylindrical Surfaces on the Light Guide Plate

AbstractWe have developed a new LED‐backlight structure which provides high efficiency with the thin profile. By applying this new optical system, power consumption can be reduced 15.5% compared with conventional thin structure as well as achieving the good luminance uniformity.

슬림형 LCD TV의 LED 백라이트 구동용 평판형 트랜스포머를 적용한 LLC 공진컨버터에 관한 연구

LCD TV의 슬림화를 위한 전원장치는 고효율 및 고전력 밀도를 요구하고 있다. 최근 LCD TV의 LED 백라이트는 소비전력이 매우 적고 수명이 반영구적이며 밝기가 뛰어나는 동시에 기존의 CCFL 보다 적은 공간을 차지해서 두께를 혁신적으로 줄일 수 있는 장점을 지니고 있다. 그리고 본 논문에서는 LED 백라이트 구동용 고주파 평판형 트랜스포머를 이용하여 LLC 공진컨버터를 제안 적용하였고 실험 결과에 대하여 서술한다. The power supply devices for reducing the size of the LCD TV are increasingly required for high efficiency and highe power density. Recently, the LED backlight of the LCD TV comes into the spotlight for LCD TV, because the conventional CCFL backlight has difficult to use constantly according to the mercury restrictions. And In this paper, the LLC resonant converter using the planar transformer for slim-type LED backlight of LCD TV is presented and verified through an experimental prototype for 47 inch LCD TVs with LED backlight system.

67.2: Compensation Methods for Local‐Dimming Backlights with RGB‐LED

AbstractIn LED backlight system with high optical independence inside a segmented block, using individually controllable RGB‐LED as light source, we can obtain the advantage of wider color gamut, lower power consumption, and wider range of LCD expression than using white‐LED. On the other hand, there are problems of influence on luminance uniformity and chromaticity uniformity caused by the device‐to‐device variations, temperature property, and age‐related deterioration in the use of RGB‐LED. Additionally, power loss and heat generation which depend on temperature property of LED forward voltage (Vf) are problems. Therefore, it is difficult to develop the LED backlight that shines uniformly with good power efficiency. To solve those problems, we develop and evaluate compensation methods such as Optical unevenness correction, Thermal feedback control, Photo‐feedback control, and LED‐applied voltage control.

Digital Micro Hinge (DMH) Based Display Pixels

Using concepts from thin-film optics we hereby present a different design for a potentially high performance display system. The system's pixel design is centered around the selective reflections and transmissions of well defined and constructed thin films on specific substrates. By computing the relevant parameters for specific thin films that can reflect and transmit only Red, Green and Blue light and marrying the result to an RGB LED backlight system a rather unique display system emerges which we termed the Digital Micro Hinge Display (DMH).

57.2: Optical Design of Phosphor Sheet Structure in LED Backlight System

AbstractA novel LED backlight unit with a phosphor sheet is proposed. The basic structure of the phosphor sheet consists of a phosphor layer with a diffusion layer on either side of the phosphor layer. The diffusion layers can reduce the chromaticity shift due to the viewing angle and incident angle of blue light.

Enhancement of the Optical Performances for the LED Backlight Systems with a Novel Dual Lens-Cap

A novel dual-cone-shaped side-emitting lens cap for High Brightness Light Emitting Diodes (HB-LEDs) is proposed for improving brightness and high uniformity of the direct LED backlight Units (BLUs) for large-sized LCD-TVs. Combining the designed lens cap with red, green and blue (RGB) chips on a Metal Core Printed Circuit Board (MCPCB), the LED module with the proposed cap is able to provide a compact white light source with unique features such as instant color variability and lower power usage, etc. The dual-cone-shaped of the proposed lens cap is designed to emit most of the light rays to the sides, only a small portion of light upward along the optical axis of the lens, providing a uniform luminance distribution and the high brightness on the backlight. In addition, a small reflective surface in semi-circular shape is designed and placed upon the proposed LED module about 10mm, the surfaces of which are attached with reflective films to increase the level of light mixing in the larger, global reflector optical box. With the structure of the LED module well designed, the LED backlight Module would be designed for the large-sized LCDTV using the fewer number of LEDs to lead to lower power consumption. The results indeed identify the attributes of the BLU, which make it possible to achieve excellent backlight performance using a direct illumination approach from the light source of “Dual-Cone-Shaped Side- Emitting Lens Cap of LEDs.”

LED Backlight Driving System for Large-Scale LCD Panels

This paper presents an LED backlight driving system for large-scale liquid crystal display panels. High efficiency, high power factor, circuit simplicity, and low cost can be achieved by using a single-stage charge-pump asymmetrical half-bridge converter. To regulate the LED current and brightness for the LED backlight system, some current sharing methods are presented and compared. The requirements for the current sharing and luminance balance among paralleled LED arrays can be satisfied while current ripple is eliminated significantly. Because of the addition of bypass diodes, an alternative current path can be offered when a single LED fails. The LED array will not be extinguished. Reliability of the LED backlight system can thus be improved effectively. A laboratory prototype has been built and tested. The simulation and experimental results are shown to verify the feasibility of the proposed method.

P‐32: LED Backlight System for Medical Imaging on LCD Monitors

AbstractNowadays products with LED backlight are entering the consumer and semi‐professional markets where wide color gamut is essential. In this paper a new LED backlight solution suitable for medical imaging application will be described where the requirements are mainly related to luminance and color accuracy and white point tuning.

P‐192: Side‐emitting LED for Direct LED Backlight

AbstractA side emitting LED for direct LED backlight system is proposed. The lens used for this side emitting LED is simple in shape and really easy to be fabricated. The design rule of the lens and the excellent simulation result of a 32 inch direct backlight system with side emitting red, green and blue LEDs are demonstrated in this paper.

LED backlight system with double‐prism pattern

Abstract— A LED backlight system with a double‐prism pattern for use in mobile phones to achieve thin and high luminance LED backlight systems is proposed. The double‐prism pattern is formed on the light guide of the proposed LED backlight system and simultaneously exhibited two optical functions: shifting of the light from the direction of the guided light toward the radiated light and controlling the directivity of the radiated light. Therefore, using the double‐prism pattern eliminates two prism sheets and a diffusive sheet, which are indispensable optical elements to exhibit the optical function that controls the directivity of light in conventional LED backlight systems. Consequently, the thickness of the proposed LED backlight system is reduced to 0.75 mm compared to that of the conventional system. A luminance of 3115 nits and a full‐width half maximum of 35° for radiated light, which are comparable to conventional LED backlight systems, were obtained.

Hybrid normal-reverse prism coupler for light-emitting diode backlight systems

For the first time to our knowledge, a hybrid normal-reverse prism coupler was formed on the bottom surface of a light guide in a LED backlight system to achieve a thin, lightweight, LED backlight system. The hybrid prism coupler (HPC) simultaneously exhibits two functions: extraction of guided light from the light guide and focusing the radiated light from the light guide, corresponding to the optical functions of the prism and diffusive sheets used in conventional LED backlight systems. Therefore, using a HPC eliminates the prism and diffusive sheets that have been indispensable optical elements in conventional LED backlight systems, which consequently reduces the thickness of the LED backlight system by 40% compared with conventional systems.

LED-backlight feedback control system with integrated amorphous-silicon color sensor on an LCD panel

— Thin-film-transistor liquid-crystal displays (TFT-LCDs) have the largest market share of all digital flat-panel displays. An LCD backlighting system employing a three-color red-green-blue light-emitting diode (RGB-LED) array is very attractive, considering its wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the high-intensity LED has problems with thermal stability and degradation of brightness over time. Color and white luminance levels are not stable over a wide range of temperature due to inherent long-term aging characteristics. In order to minimize color point and brightness differences over time, optical feedback control is the key technology for any LED-backlight system. In this paper, the feasibility of an optical color-sensing feedback system for an LED backlight by integrating the amorphous-silicon (a-Si) color sensor onto the LCD panel will be presented. To minimize the photoconductivity degradation of a-Si, a new laser exposure treatment has been applied. The integrated color-sensor optical-feedback-controlled LED-backlight system minimized the color variation to less than 0.008 Δu'v' (CIE1976) compared to 0.025 for an open-loop system over the temperature range of 42–76°C.

41.1: A Thin LED Backlight System with High Efficiency for Backlighting 22‐in. TFT‐LCDs

AbstractA TFT‐LCD with RGB LED‐Backlight has become well‐known as wider color reproduction. By matching the transmissive spectra of color‐filter to high‐power red, green and blue (RGB) LEDs radiation, wider color reproduction and higher brightness have been achieved. But it has been difficult to mix the RGB light of high‐power LEDs without a loss of light until the light is introduced into the LC‐panel. We have developed a new LED‐Backlight system that provides an optical efficiency of 72%. This efficiency is 1.4 times the previous LED‐Backlight with a light guide. We applied this new LED‐Backlight to a 22‐in. XGA‐Wide TFT‐LCD and achieved a brightness of 540cd/m2 and color reproduction of 105%.

43.3: High‐efficiency Slim LED Backlight System with Mixing Light Guide

AbstractWe have developed a novel optical system for an edge‐lit LED backlight. The system uses high‐power red, green and blue LEDs and has a minimum thickness despite the arrangement for color mixing. The components of the system have been optimized enabling high optical efficiency while maintaining low cost and good manufacturability. Furthermore, conceptually the system is very close to the existing CCFL backlights and allows re‐use of the existing components and infrastructure.