Backlight Design Research Articles

66.3: Design of Color Backlight for High Efficiency Display using Optical Waveguide Gratings

AbstractWe report a novel backlight with waveguide gratings instead of using color filters to reduce power consumption. The waveguide gratings enable the red‐green‐blue (RGB) light propagate separately and be emitted toward the respective pixels unidirectionally. Selective emitting rate and direction is obtained by optimizing the grating geometry. This device shows potential for micro‐display.

Review Paper: Diffractive backlight technologies for mobile applications

Abstract— Liquid‐crystal‐display backlight units have developed in their conventional configuration into very efficient and uniform components that allow the display to present a high‐quality image to the user. Developing the backlight unit itself further faces a challenge of diminishing returns to the investment in innovation. A system‐level redesign is required for the entire display module, and diffractive alternatives to the backlight design can allow a more‐energy‐efficient design for the display. This review concentrates on small‐to‐medium displays because diffractive backlight studies have also centered in this class of displays. The state of the art of backlight design is summarized and the motivation for energy‐efficient system design is outlined. The theoretical basis of diffractive backlights is given, and key research studies in the area of diffractive backlights are reviewed. Finally, a discussion on the performance and future outlook of diffractive backlights completes the paper.

Mobile display backlight light guide plates based on slanted grating arrays

Modern mobile communication devices have user interfaces that are dominated by high-quality displays. Increased multimedia use imposes high demands on the design of display modules, as the content available for mobile use becomes visually richer. Especially the power dissipation of the display can limit the amount of time available for multimedia consumption and interaction. In the mobile liquid-crystal display (LCD), the energy efficiency is determined by the backlight design. State-of-the-art backlights direct white light through a display subpixel array, with high uniformity and up to 90% efficiency in white light output. Therefore, it is difficult to obtain system-level energy savings by improving the backlight design alone. Diffractive backlights have recently been proposed to reduce the power dissipation of the display module, and slanted grating arrays are among the enabling optical features that allow for reduction in power dissipation beyond what is available in the state of the art. By the use of diffractive grating arrays, the required primary color (red, green, or blue) is directed through the LCD subpixel array with geometrical registration, instead of flooding the whole LCD with white light and filtering the primary colors through the subpixel color filter array. We present a study on grating structures based on slanted grating arrays fabricated in high refractive index materials. The grating design principles and grating outcoupling results are provided, and an outline of a new embedded system design is given. Emphasis is on grating array design aspects for future energy-efficient display system design. The results show that savings in power consumption can be expected with advanced display system design based on embedded slanted grating array backlight light guide plates.

LED backlight designs with the flow-line method

An LED backlight has been designed using the flow-line design method. This method allows a very efficient control of the light extraction. The light is confined inside the guide by total internal reflection, being extracted only by specially calculated surfaces: the ejectors. Backlight designs presented here have a total optical efficiency of up to 80% (including Fresnel and absorption losses) with an FWHM below 30 degrees. The experimental results of the first prototype are shown.

Thermal Design of LED Backlight in High Ambient Temperature

Different from common commercial liquid crystal displays (LCDs), LCDs in military applications have some special requirements including high luminance, wide operating temperature, and night vision compatibility. This paper designs a direct-lit LED backlight for a 5 in×5 in LCDs and puts forward three solutions for heat dissipation. The simulation results show that the solution of 17×17 LED array on common opening FR4 PCB can satisfy the requirement.

20.3: All‐In‐One Monitor Capable of Power‐over‐Ethernet or USB

AbstractIncreased display efficiency gives device manufacturers more freedom to design new, previously unfeasible, low power devices. By combining an energy efficient backlight design with an efficient light source, display powers can be lowered to levels where a power source other than alternating current AC mains becomes feasible. Examples of a USB powered monitor in the mainstream size, as well as a Power Over Ethernet POE All‐In‐One Thin Client/Monitor device are demonstrated with today's technologies as a combination of efficient LEDs, reflective polarizers and low power LCD panels.

Cost effective design and implementation of scanning-based LED backlight for LCD module

Blurring effects in liquid crystal display can be observed in motion pictures if the response time of the liquid crystal molecules is not fast enough. In this study, a cost-effective architecture for backlight control system is proposed with scanning based method. A backlight control process employed with sequential lighting of the backlit pixels to reduce the blurring effects on LCD. Based on the sequential control, a 42-inch white light backlight module system with 1440 LED devices can be driven by only two driver chips. The prototyping backlight system had been implemented within one PCB in success. The measurement results from the laboratory demonstrate that the backlight system can save power dissipation and provide enough brightness for LCD. The proposed backlight system can be not only to reduce the implementation cost but also to shrink the driving broad size. The implementation cost can be reduced by about 70% compared with the conventional architecture.

A color‐filterless LCD with RGB LED and lenticular‐lens arrays

A direct‐lit liquid crystal display that does not use color filters is proposed. A backlight unit that employs compartmentalized RGB LED and lenticular‐lens arrays is used instead of color filters to direct the RGB LED lights into the RGB subpixels. The color‐filterless LED backlight design, simulation, and experiment results are presented.

P‐79: HSP: A Hybrid Simulation Platform for Backlight Dimming in TFT‐LCDs

AbstractA general and comprehensive hybrid simulation platform(HSP) is developed for conveniently evaluating and optimizing the backlight design and driving schemes in TFT‐LCDs to achieve low power and excellent image quality. It incorporates a range of capabilities from the early backlight optical simulation to the performance evaluation and optimization at the system level for the design of almost all kinds of LCD backlight systems. The HSP is then used to optimize and evaluate a local dimming scheme based on edge‐type LED backlight technology for a 14.1′W TFT‐LCD panel, and the simulation and analysis results are presented.

Optical design of LED edge-lit backlight based on molecular dynamics method using a random/regular composite distribution

A dot generation scheme for random/regular composite distribution is developed based on the molecular dynamics (MD) method for application in light guide design. This is done by introducing random r-cut values in the force field acting between dots. The results indicated that the developed scheme can effectively randomize a regular distribution by increasing the random component of the r-cut value. In addition, for a composite distribution, in order to obtain a smooth distribution across the random/regular distribution interface, there cannot be a large difference between the expected r-cut value for these two distributions; otherwise, a distinct linear strip will occur. Finally, two practical examples are presented. One randomizes an already optimized dot distribution in a regular arrangement. The other uses a composite distribution generated by the present scheme which is substituted into the optical software to perform the optical optimization. These two examples prove the validity of the present scheme and its efficient application in the optical design of light guides.

Contrast gain and power savings using local dimming backlights

Abstract— The contrast and power consumption of today's liquid‐crystal displays (LCDs) can be improved substantially by introducing (local) dimming backlights. In fact, infinite dynamic contrast and power savings of well over 50% have been claimed for such displays. Because these claims are generally made for very specific backlight designs and image content, the contrast gain and power savings are quantified as a function of the number of backlight segments for a large variety of image content.

P‐108: Backlights in Mobile Display Power Management

AbstractPower efficiency of a mobile multimedia display relies on power management methods that affect the on‐state of the display. Other means of power management in mobile devices are dependent on managing the transitions between the off‐state, power‐saving mode, and on‐state effectively. These methods do not readily apply to modern consumption of mobile multimedia, as the display is in the on‐state continuously. A conceptual display system power management model was developed. The model was used to estimate the efficacy of a new diffractive optical mobile display backlight concept, and the effect of the display backlight design especially was found to result in considerable power savings in modern mobile multimedia displays.

Brightness management in a direct LED backlight for LCD TVs

Abstract— A method of calculating the luminance and luminance uniformity of a bottom LED backlight is proposed and demonstrated. Both the power consumption and brightness uniformity as a function of screen brightness, screen size, backlight thickness, transmittance of the LCD panel, reflective cavity efficiency, gain, cone angle of the enhancement films, LED array configuration, and the average luminous flux, radiation pattern, and input power of individual LEDs. Moreover, a 42‐in. LCD TV using this backlight design approach was fabricated. The bottom backlight incorporates an array of RGGB 4‐in‐1 multi‐chip LEDs within a highly reflective box behind a diffuser and a dual brightness‐enhancement film. The brightness uniformity can be predicted within an accuracy of 94% and the luminance level within an accuracy of 96%.

Optical Simulation of Direct-type Backlight Unit for Medical Application

In this study, it was investigated about optical simulation in direct-type backlight design. Direct-type backlight has been used high-brightness backlight such as medical LCD application. The key parameter in designing direct-type backlight was consists of three geometrical dimension such as the distance of two lamps, the gap of lamp and reflection plate and the number of lamps. It has many of variations in optical design and it causes the different properties in backlight system. It shows the best values of above parameters; 26 mm of the distance of two lamps, 4.5 mm of the gap of lamp and reflection plate and 16 lamps. And we produced the specimen as above condition, and acquired good result in backlight such as the value of the brightness is 6423 nit in center of emission area and less than 5 % in brightness uniformity. It shows the effective ways of designing backlight system using optical simulation method for medical LCD application.

Ultra-Thin Design of Large Backlight Module Used in Illuminating Advertising Pictures

At present, the large backlight modules, used in illuminating advertising pictures, are designed and developed in various specifications, whose common goal is to try to manufacture thinner backlight modules and produce more uniform illumination. The currently well developed backlighting technology for liquid crystal displays (LCDs) can be transformed and used in such an area. However, the design of edge-lit backlight with size of over 1 square meter has great difficulties in eliminating the phenomenon of non-uniform illumination. In this paper, the application of Bezier curve in the simulating the dot pattern on the bottom of light guide is presented, which directly determines the final light extraction efficiency and illuminating uniformity. Taking the RMS deviation of illuminance values at several sample positions as the merit function, the shape of Bezier curves can be smoothly changed, so that the dot radius can be optimized in a fast and efficient way. Such an optimization procedure uses only two variables and has a fast convergence. As an example, a large light guide, 800mm×1000mm in size, was designed by applying the Bezier method, and the final uniformity of 70% was achieved. The most prominent feature in such a method is that the thickness of designed light guide can decrease to 5 mm. In sum, the large sized edge-lit backlight can be designed in a short optimization period by simulating the dot radius distribution in a shape of the Bezier curve.

Focus on lasers and optics

Focus on lasers and optics

P‐67: Region‐Partitioned LED Backlight Design for Field Sequential Color LCD

AbstractIn this paper, a 7‐inch backlight module consisting of ten isolated micro‐structured linear light pipes and two side‐collimating bars was developed with serial full‐color LEDs as light sources for a field‐sequential‐color liquid‐crystal display (FSC‐LCD) system. The collimating lighting system not only yields a narrow angular light distribution, but also effectively diminishes color dependence in the scanning backlight for FSC applications. The crosstalk of the light from each linear light pipe leaking out to the neighboring divisions was measured; meanwhile, the divergent angles of extraction light were well controlled to about ±17° and ±30° at two orthogonal directions respectively.

P-239L: Late-News Poster: E-2D Advanced Hawkeye: Primary Flight Display

This paper is a response to the challenge of providing a large area avionics display for the E-2D AHE aircraft. The resulting display design provides a pilot with high-resolution visual information content covering an image area of almost three square feet (Active Area of Samsung display = 33.792cm × 27.0336 cm = 13.304″ × 10.643″ = 141.596 square inches = 0.983 sq. ft × 3 = 2.95 sq. ft). The avionics display application, design and performance being described is the Primary Flight Display for the E-2D Advanced Hawkeye aircraft. This cockpit display has a screen diagonal size of 17 inches. Three displays, with minimum bezel width, just fit within the available instrument panel area. The significant design constraints of supporting an upgrade installation have been addressed. These constraints include a display image size that is larger than the mounting opening in the instrument panel. This, therefore, requires that the Electromagnetic Interference (EMI) window, LCD panel and backlight all fit within the limited available bezel depth. High brightness and a wide dimming range are supported with a dual mode Cold Cathode Fluorescent Tube (CCFT) and LED backlight. Packaging constraints dictated the use of multiple U shaped fluorescent lamps in a direct view backlight design for a maximum display brightness of 300 foot-Lamberts. The low intensity backlight levels are provided by remote LEDs coupled through a fiber optic mesh. This architecture generates luminous uniformity within a minimum backlight depth. Cross-cockpit viewing is supported with ultra-wide field-of-view performance including contrast and the color stability of an advanced LCD cell design supports. Display system design tradeoffs directed a priority to high optical efficiency for minimum power and weight.

P-77: Novel Reflectors for LCD Backlights

A new reflector film has been developed for LCD backlights. The performance advantages of this new film are described including higher reflectivity, improved color and higher blue reflectivity. The higher performance of this new reflector film allows new approaches to backlight design leading to higher performance and light utilization. Improved performance of this reflector in commercial direct-view and edgelit backlights is discussed and excellent environmental stability is described.

38.4: New Concepts of LCD-TV Backlight Design with Variable Lamp Pitch

A novel backlight technology is presented for the backlight unit design. The main thinking refers to the human eyes sensitivity to brightness uniformity to modify the current rule. This approach brings better cost-benefit and yields close picture quality. In the following content, the approach was applied, and CMO 27-inch LCD-TV was illustrated as an example.