Backlight Module Research Articles

High-Performance Local Dimming Algorithm and Its Hardware Implementation for LCD Backlight

The local-dimming backlight has recently been presented for use in LCD TVs. However, the image resolution is low, particularly at weak edges. In this work, a local-dimming backlight is developed to improve the image contrast and reduce power dissipation. The algorithm enhances low-level edge information to improve the perceived image resolution. Based on the algorithm, a 42-in backlight module with white light-emitting diode (LED) devices was driven by a local dimming control core. The block-wise register approach substantially reduced the number of required line-buffers and shortened the latency time. The measurements made in the laboratory indicate that the backlight system reduces power dissipation by an average of 48% and exhibits no visible distortion compared relative to the fixed backlighting system. The system was successfully demonstrated in a 42-in LCD TV, and the contrast ratio was greatly improved by a factor of 100.

Optimizing angular placements of the LEDs in a LCD backlight module for maximizing optical efficiency

This study aims to optimize angular placements of the LEDs with novel cone-shaped caps for achieving high optical efficiency in an ultra-thin, directly-lit RGB LED backlight unit (BLU) for large-sized LCD-TVs. This novel lens cap is used as a diffuser with the purpose to gain higher efficiency and provide satisfactory uniformity over a display panel. To this aim, the outer surface of the novel lens is coated with aluminum for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, finally to the output plane. Since the emitted white light from LEDs result from color-mixing of three individual RGB chips in a LED package, the addition of the LED cap however deteriorates the aforementioned expected color mixing. The optimal design on angular placements of LEDs presented in this study for satisfactory color-mixing and emission uniformity is achieved by necessary optics simulations via TracePro, followed by utilizing an intelligent numerical optimization technique, genetic algorithm (GA). The design parameters for GA optimization are different combinations of LED placement angles in a backlight module. Favorable color balance is shown achievable in terms of high low color difference resulted. Finally, experiments are conducted, which successfully validate the expected performance of color balance and emission uniformity for a novel cone-shaped LED lens with optimized angular placements in a large-area backlight module.

P.50: Design of a Novel Hybrid Light Guide Plate for Viewing Angle Switchable Backlight Module

AbstractWe introduce a viewing angle switchable backlight module, which consists of a hybrid light guide plate and dual‐light sources on the same layer. Comparing with the conventional backlight module, the on‐axis luminance of the narrow viewing angle improved 4.9‐times and the half‐luminance angle decreased 11 degrees in the horizontal direction. When using the wide viewing angle mode, the on‐axis luminance improved 2‐times and the half‐luminance angle improved 56 degrees in the horizontal direction.

P.81: A Time‐Multiplexed Dual‐View Display Using Blue Phase Liquid Crystal

AbstractA time‐multiplexed dual‐view display device using a blue phase liquid crystal is proposed. In this design, a vertical field switching blue phase liquid crystal display (VFS‐BPLCD) panel is used to achieve high transmittance and fast response. Combined with a directional backlight module, this device can present two different images to viewers sequentially. The proposed device has advantage in full spatial resolution.

An effective system for parameter optimization in photolithography process of a LGP stamper

In the current thin-film transistor liquid crystal display industry, the light guide plate (LGP) of the backlight module has become thinner and smaller, and the backlight module needs to be illuminated uniformly and effectively. The parameter setting for the photolithography process of a LGP stamper often relies on the engineers’ experiences by means of trial-and-error or design of experiment to obtain a suitable and more reliable process parameter setting, which requires a large amount of time, manpower, and cost. This research proposes a novel two-stage optimization system for photolithography process integrating the Taguchi method, back-propagation neural networks, genetic algorithms, particle swarm optimization, and related technologies to effectively generate optimal process parameter settings. The first stage is to reduce the process variance. The second stage is to find the final optimal process parameter settings for the best quality specification. Experimental results show that the proposed system can create the best process parameters which not only meet the quality specification for the micro-dots on the photoresist, but also effectively enhance the overall process stability.

Time-Multiplexed Dual-View Display Using a Blue Phase Liquid Crystal

A time-multiplexed dual-view display device using a blue phase liquid crystal is proposed. In this design, a vertical field switching blue phase liquid crystal display (VFS-BPLCD) panel is used to achieve high transmittance and fast response. Combined with a directional backlight module, this device can present two different images to viewers sequentially. The proposed device has advantage in full spatial resolution.

A Novel Continuous Extrusion Process to Fabricate Wedge-Shaped Light Guide Plates

Backlight modules are key components in thin-film transistor liquid crystal displays (TFT-LCD). Among the components of a backlight module, the light guide plate (LGP) plays the most important role controlling the light projected to the eyes of users. A wedge-shaped LGP, with its asymmetrical structure, is usually fabricated by an injection proces, but the fabrication time of this process is long. This study proposes a continuous extrusion process to fabricate wedge-shaped LGPs. This continuous process has advantages for mass production. Besides a T-die and rollers, this system also has an in situ monitor of the melt-bank that forms during the extrusion process, helping control the plate thickness. Results show that the melt bank has a close relationship with the plate thickness. The temperature of the bottom heater and roller was adjusted to reduce the surface deformation of the wedge-shaped plate. This continuous extrusion system can successfully manufacture wedge-shaped LGPs for mass production.

Optical Microstructure Design Optimization for Display Backlighting

This study proposes an innovative design method for functional optical film microstructures used in displays and applies this design to LCD backlighting to replace multi-layer optical film functional integration with composite optical film. We design a novel optical film microstructure based on light uniformity and wide-angle lumination distribution and determine the optimal optical microstructure parameters by combining the global optimization of a genetic algorithm with ray tracing. The purpose of this study is to develop substitutes for traditional multi-layer prism brightness enhancers and light-diffusing film stacks and to examine the structural changes during calculations and summarize the characteristics. In this study, we focus on determining the optimal light uniformity of new optical film microstructures. The seven-inch LED backlight module of the method proposed in this study achieved 94.59% uniformity and 168° lumination distribution while reducing thickness by 66% to 82% compared to a traditional multi-layer optical film stack.

狭缝光栅分光特性及其对视区的影响

Redistributing parallax images by light directing element such as grating is one of the most important methods to achieve 3D display.This paper gives an introduction of how parallax barrier works to realize 3D display.The mathematical model of beams out of multi-period of barrier has been built to explore the roles played by barrier and width of sub pixel.Software to simulate the optical field in front of the 3D display has been developed.Both property of view zone and brightness of the display should be considered in order to get better 3D result.This study shows that the slit ratio for parallax barrier should between 0.2 and 0.3.In the process of prototype making the scale was set to 0.25.Particular bright backlight module was applied to compensating the lower brightness caused by lower scale and the display got a satisfactory result.The result has directive meaning for design of 3D display based on parallax barrier.

Fabrication of flexible light guide plate using CO2 laser LIGA-like technology

The liquid crystal display (LCD) needs the back light module (BLM) for the light source. The light guide plate (LGP) is the main component of BLM to spread light source to the whole LCD surface and requires for the generation trend of lightweight, easy to carry, and bendable for LCD. In this article, we have demonstrated the fabrication of flexible LGP using CO2 laser LIGA-like technology which includes the laser ablation of micro-groove polymethylmethacrylate (PMMA) master mold, pouring polydimethylsiloxane (PDMS) to the mold and casting the micro-groove microstructure for flexible LGP application. Different laser powers and micro-groove pitches were used to ablate the PMMA mold with varied groove depths and taper angles. Optical microscope was used to examine the morphology and profile of the final bendable LGP microstructure. Under the varied laser power of 1---12 W, the mean taper angles of PMMA micro-grooves ranged from 28° to 70° and the etching depths were from 44.5 to 281.8 μm. The flexible PDMS LGP had good microstructure duplication after casting. The optical uniformity and luminance of flexible LGP was concerned with structure of micro-grooves and measured using BM9 luminance meter. The maximal light uniformity and average luminance of LGP at some microstructure reaches 75 % and 119 cd/m2, respectively.

66.2: Optimization of LED Arrangement for Extending LED Binning Range in Backlight System

AbstractIn this paper, an analysis method was developed to calculate the optical properties of direct‐emitting backlight systems, which expands the usage of bins. The method based on computing the radiance distribution from the measured light spreading function and spectrum of light‐emitting diode (LED). The calculation procedure includes linear spectral superposition and color difference evaluation. The accuracy of this method was verified by a real backlight module, which introduced the remote phosphor backlight system. This structure could have more benefits than the traditional one, including thinner thickness, longer life time, and wider LED bins. The conditions of acceptable color deviation values could be simply obtained, and the different binned LEDs could be efficiently used to reduce cost and achieve the wider binned‐LEDs application purpose.

LED Backlight Module by a Lightguide-Diffusive Component With Tetrahedron Reflector Array

In our previous work, IEEE/OSA Journal of Display Technology, February 2012, we examined the luminance and uniformity characteristics of a newly invented secondary optical lens with a wide emission angle called a “lightguide-diffusive component”. The lightguide-diffusive component is designed for thin direct LED backlighting applications. The LED backlight module is composed of at least an LED light source, a secondary lightguide-diffusive component with a micro-structure reflective bottom surface, and a flexible printed circuit (FPC) for LED lighting without a brightness-enhanced film (BEF). Through this lightguide-diffusive component, the emission profile of a single LED is modified to provide better illumination and more uniformity. In this work, the micro-structure reflective bottom is redesigned to be shaped like a Tetrahedron Reflector Structure Array instead of a triangle cylinder structured array, resulting in a more uniform spatial light energy distribution on the emission plane of the LED backlight. The simulation results show an increase in the uniformity ratio with the new design from 72% to 76%, a 4% improvement, the angle of the luminous intensity is increased from 98 deg to 112 deg, a 14 deg improvement, a decrease in the luminance is from 9024 nits to 8551 nits, an impairment of 5%, and a decrease in the volume of the micro-structure reflector from 1.154 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 0.767 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , a 33.5% volume reduction (cost saving).

P‐65: A Novel Highly CoNimating Backlight Module Using a Double Wedge‐Shaped Light Guide Plate

AbstractA novel highly collimated backlight module transforming a point light source into a planar light source by means of a double wedge‐shaped light‐guide plate (LGP) was designed. The uniformity of spatial luminous can reach 80.5% at view cone of ±1.8 deg. The Gray‐half‐tone technology can be used to fabricate the microstructures for mass productions.

Evaluating Process Yield for LED Assembly under Undetected Process Parameter Change

AbstractThe technology of light emitting diode (LED) assembly has become more popular due to the high demand for LED backlight modules, which can provide desirable characteristics such as a wide color gamut, a high dimming ratio, a long lifetime, and high power efficiency. For LED assembly processes, the distance between LEDs is one of the key parameters because the uniformity of an LED backlight module can be affected by it. In order to obtain good optical performance of an LED backlight module, the process yield of the parameter needs to be controlled well. Conventionally, process yields of LED assembly processes are evaluated using typical capability index methods under the essential assumption that the processes are stable. However, some inevitable process parameter changes regarding the distance between LEDs might exist on the shop floor. In order to evaluate the process yield more accurately, this paper presents an accommodated capability index method for process yield evaluation under undetected process parameter changes. For illustration purposes, an application is presented.

Polarized backlight with constrained angular divergence for enhancement of light extraction efficiency from wire grid polarizer

Efficiency of liquid crystal displays highly depends on the amount of polarized light emerging from the backlight module. In this paper, a backlight architecture using a nanoimprint wire grid polarizer for polarization recycling is proposed and studied, in which the extraction efficiency of polarized light is the major concern. The backlight module is composed of the stack of a wire grid polarizer, a lenticular array and a light guide plate. The light guide plate features interleaving v-groove and trapezoidal ridge coated with aluminum on the top surface, and scattering dot array on the bottom. The angular divergence of emerging light from the light guide plate can be well constrained so as to exploit the angular range with the best transmission of polarized light for the wire grid polarizer. The prototype of a 2.5-inch module has demonstrated an angular divergence of 48°. The overall extraction efficiency of polarized light enhanced by 21% and uniformity of 76% have been achieved.

LED Backlight Module by Lightguide-Diffusive Component

This study examines the luminance and uniformity characteristics of a newly invented secondary optical lens, called the “lightguide-diffusive component,” which has a wide emission angle and is designed for thin direct LED backlighting applications. The LED backlight module is composed of, at the very least, a light source, a secondary lightguide-diffusive component with a newly designed micro-structure having a reflective bottom surface, and a flexible printed circuit (FPC) for LED lighting. This lightguide-diffusive component modifies the emission profile of a single LED to provide better illumination and greater uniformity. The newly designed secondary optical lens module is shaped to cover the LED array, resulting in a more uniform spatial light energy distribution on the emission plane of the LED backlight. The uniformity ratio for the new design shows an increase of 24%, from 60% to 84%, and the luminance a 23.29% improvement, from 10 000 nits to 12 329 nits.

Compound Optical Film Using Gray Scale Mask Embedded with Microvoids

This study presents a compound optical film to improve luminance and uniformity to apply in side-LED (light-emitting diode) backlight module. LIGA (lithographie galvanoformung abformung) technology, soft lithography, and homemade gray scale mask were combined to fabricate microlens array. Optical film with variable size microlens array embedded with microvoids was designed and manufactured. FRED software was used to simulate optical performance. Microvoids were quantitatively embedded in the PDMS (polydimethylsiloxane) optical film. Under the quantitative control of air pressure, those microvoids inside the optical film can cause light diffusion. The compound optical film with embedded microvoids, multiaspect ratio, and variable size microlens array can be fabricated quickly without substrate. Luminance colorimeter BM-7A from TOPCON was used to carry out the optical measurement. According to the measured data, the compound optical film with embedded microvoids can enhance the luminance up to 5% and the uniformity up to 6.5% ~ 8.4%. The optical efficiency can be improved via the compound optical film.

均匀照明LED背光板设计

Currently,more and more liquid crystal displays are towards to the low-power,which the effective method is reducing the number of LEDs as the light source.However,as the decrease of LED pixel,hot spot will increase fast.To solve above problem,without changing the distance between LED and guide plate,and with increasing the distance between LED and LED as well as incident angles of guide light plate,light in guide light plat is completely mixed by using this method,and light uniformity is much more improved.Hot spot in the LED backlight module are also solved.This research has good significance for LCD display.

一种新颖微型液晶显示器背光设计技术

Aiming at the problem that the current micro-LCD brightness can not meet the brightness requirements of airborne helmet-mounted displgy,a novel backlighting structure form and design principle were proposed,and the optical system was designed using the CODEV software.The light distribution effect of the backlight module was simulated using the LIGHTOOLS software.The results show that,when taking 85 lm green LUXEON Rebel LEDS as the light source,its output brightness is close to 160 000 cd/m2,uniformity is greater than 85%,and power consumption is only 1.25 W,which meets the requirements of the airborne helmet-mounted display.

Diffuser Films and Optical Performance in LCDs

Diffuser technology is a vital differentiator in the optical performance of LCDs. The authors outline some common approaches for backlighting and film stacks and explain how different types of diffuser films are employed. They also describe how micro‐lens diffusers in LCD backlight modules can provide performance that is 10% better than that of bead‐filled coated PET diffusers and equivalent to that of coated micro‐lens PET diffusers.