Backlight Unit Research Articles

P‐214: Late‐News‐Poster: Development of Ce3+ Activated Yellow‐Orange Nitride Phosphor for Various Applications

(La,Y)3Si6N11:Ce3+ (LSN) phosphor has been used for white LEDs in back light units (BLUs). We have succeeded in developing LSN phosphors with wide color variations, less thermal quenching and any other luminescence properties. We expect that LSN phosphors will be also used for lighting and laser devices.

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.

P‐97: Applications of Metal Halide Perovskite as Passive and Active Light Emitting Materials

Metal halide perovskites are promising materials for display applications as phosphors and active layers in light‐emitting diodes. Here, we briefly review the physical properties that make them suitable in such products, namely their high absorption and emission coefficients, combined with good charge transport properties and ease of fabrication. Then, we report on the development of green perovskite emitters and the fabrication of down‐conversion films for backlight units (BLUs). Finally, we summarise our recent development in perovskites LEDs, showing how we have reached commercially‐relevant efficiencies for each color channel.

64‐3: Simulation of Beam Shaping by Micro‐textures for Curved Displays

We simulate the guiding and out‐coupling of light in strongly curved backlight units with edge illumination using a 3D ray‐tracing tool with custom light emission and scattering features. The impact of the display curvature is assessed regarding the uniformity and angular characteristics of light outcoupling in a complex backlight with position‐dependent bottom roughness, a diffuser element and a textured brightness enhancement film.

45‐2: Distinguished Paper: Ultra‐narrow Border Display with a Cover Glass Using LCDs with a Polyimide Substrate

We propose a novel plastic Liquid crystal display (LCD) with an ultra‐narrow‐border. As the most significant improvement, the four borders of the LCDs can be folded to wrap the backlight unit. This LCD was based on various new techniques, including the use of plastic substrates, processing of polarizer films, control of the neutral surface of a bending component based on the sealant width, and the use of a cover glass with a lens effect. We believe that these novel LCDs will be useful for numerous new applications.

Effect of functionality of thiol on the optical properties of liquid crystals/polymer composite films

ABSTRACT Optical diffusers with high transmission, high haze and excellent diffusing ability are widely needed in backlight unit (BLU) of liquid crystal displays (LCDs). However, there are still drawbacks in the particles-doped optical diffusers, including the distribution of the scattered particles due to agglomeration of particles and complex coating process. In this paper, polymer/liquid crystal (LC) composite films which are based on the epoxy resins, polyamine (PA) and varied thiol monomers were firstly prepared by thermally initiated polymerisation. The morphologies and optical properties of the composite films were systematically investigated. By controlling the functionality of thiol in the system of epoxy resins/thiol/PA/LCs, as the light scattering of anisotropic LCs and isotropic polymer framework is both achieved in the optical diffusers, good diffusing ability and high visible transmission (total transmission >96.0% and transmission haze > 95.0%) are obtained.

Infrared thermography as evaluation method of a faulty status of a LED LCD TV

AbstractThe paper presents the application of infrared thermography in the detection of anomalies (hotspots) that may lead to defects of the backlight unit, which are not yet noticeable in the visible part of the electromagnetic spectrum. It is shown on a practical example of an LED LCD TV how hotspots at the maximum level of brightness led to the failure of one element of the LED backlight segments in 2 years time. Once the faulty element was detected, brightness was reduced in order to preserve the remaining LED elements. Infrared thermographic analysis of the faulty state was repeated and compared with measurements of photometric values. The thermal analysis results, before and after failure, are displayed in line at the area of the LED elements and in 3D on the screen surface. The photometric analysis was done on the full‐screen area in each of the RGB channels and then followed with in‐detail measurements on 200 points. As most photons emitted from the diode are dispersed to the sides of the display due to the lens mounted on top of each LED and other optical elements, data obtained by photometric means are not as precise in the positioning of faulty LEDs, as ones obtained by thermal inspection.

Study and reduction of waterfall effect caused by dimming backlight in LCD based on amorphous silicon TFT

Liquid crystal display (LCD) is one of the most popular displays nowadays, and the amorphous silicon thin film transistors are adopted in LCD as active devices due to the low cost, low process issue and high stability. In the LCD device, the backlight unit consumes almost one third of the power of the LCD device. Therefore, reducing backlight power consumption is important to lower the total power consumption. Dimming backlight, which decreases brightness of the backlight and thereby reduces power consumption without affecting the display quality, is the most popular and effective method. However, because of photon assisted current effect of amorphous silicon, the conductivity of the amorphous silicon is different when backlight unit (BLU) turns on and off, which will cause a waterfall phenomenon. Compared to the traditional 4‐mask process, the difference between AS tail and N+ tail in novel 4‐mask process is smaller. The waterfall phenomenon of novel 4‐mask is not obvious but still visible. In this paper, we analyzed the mechanism of waterfall effect and modified the novel 4‐mask process to solve this issue. By combining capacitance extraction and charging simulations, we simulated the variation of grayscale caused by backlight switching. It was shown that there were about 4 gray levels of brightness change under 24 gray levels. Then we examined the cause of the formation of AS tail and N+ tail, and reduced the difference between AS tail and N+ tail by changing the process, which effectively modified the waterfall issue.

Optically Tunable Bifunctional Structures Fabricated by Hybrid Imprint‐Photo Lithography (HIPL)

AbstractOptically tunable bifunctional structures are created by hybrid imprint‐photo lithography (HIPL), which is a combination of photolithography and soft lithography via a structured photomask. Prismatic patterns are formed on a flexible photomask, and the structured photomask is exploited as an imprint mold to create two‐layered microstructures that show a tunable refraction property. Fabricated microstructures, such as the perpendicularly aligned cross‐prismatic island (PAC‐PI), show optically dual functionality that originates from each optical property of the upper and lower layers in two‐layered structures with symmetric light collimation in the vertical and horizontal axes along both directions of the upper and lower prismatic layers, whereas a single conventional prismatic film shows only one‐axis collimation. Moreover, tunability of the light collimation, which can be modulated by varying the area ratio of the upper and lower layers from 80% to 20% using optical simulation, is demonstrated. Such optically tunable bifunction on a single sheet could potentially reduce the number of required optical sheets, such as the liquid crystal display backlight unit (LCD BLU). This new hybrid lithography process could provide a potential pathway to construct highly complex optical components, such as planar waveguide, microlight emitting diode, virtual reality/augmented reality, and holographic display devices.

Heuristic Hybrid Bacterial Foraging Algorithm for the Pose Detection of Backlight Units

The liquid crystal display module (LCM), which is used to show images and videos, is the most significant component of LCD TV. To assembly a LCM, the open cell should be put exactly into the backlight unit (BLU). To accomplish the task quickly, this paper proposes a heuristic method to detect the pose of the BLU. Firstly, the coarse rotation angle of a BLU is detected with the dominant orientations (DOs). The DOs are obtained with the gradient orientation statistical histograms based on a region growing strategy. Secondly, the optimal pose of the BLU is searched with the heuristic hybrid bacterial foraging algorithm (HHBFA) which can avoid the time consuming exhaustive search (ES). HHBFA is designed according to the distribution characteristics of the similarity to find the optimal pose. The proposed method is evaluated on an image database acquired from the assembly lines. Experimental results prove the efficiency of the proposed method and highlight the superiority of it.

Ultra‐narrow border display with a cover glass using liquid crystal displays with a polyimide substrate

AbstractPlastic liquid crystal displays (LCDs) termed sheet LCDs with transparent polyimide (PI) substrates were constructed. There is a lot of potential to expand the use of these LCDs in LCD applications. Herein, we investigated a structure for sheet LCDs such as high‐density main post spacers (PSs) and PI substrates with the aid of a barrier layer to control the residual stress and protect the liquid crystal from moisture.Drawing on this, we propose an ultra‐narrow border LCD that makes of the developed sheet LCDs. The most significant improvement is that the four borders of the LCD can be folded to wrap the backlight unit. This LCD was based on various new techniques, including the use of plastic substrates, processing of polarizer films, control of the neutral surface of a bending component based on the sealant width, and the use of a cover glass with a lens effect. We believe that these novel LCDs will be useful in numerous new applications.

Automated Defect Inspection Algorithm Incorporated Spectral-Domain Optical Coherence Tomography for Optical Polarizing Thin Films

Optical polarizing thin film is an optical filter enables light waves of a specific polarization pass through while blocking light waves of other polarizations. Optical polarizing thin films control the brightness of back-light unit for LCD (liquid crystal display) panel, which is essential to produce LCD modules. Defect inspection of polarizing thin films is an important feature during the manufacturing process that is helpful to improve the product quality. In the current study, an automated defect inspection algorithm is introduced and incorporated with a well-known non-destructive and non-contact optical inspection method called spectral domain optical coherence tomography (SD-OCT) to pre-identify defective sub-surface as well as top-surface locations of optical polarizing thin films Polarizing thin films employed in this study consist of 6 layers. The tomographic information, layer information, and defective locations were sufficiently identified through the SD-OCT system owing high-axial resolution. The acquired results indicate the possible application of the proposed system in optical polarizing thin films for the quality assurance.

Design, manufacturing and experimental validation of a bonded dual-component microstructured system for vertical light emission

This article presents a bonded dual-component microstructured planar device made of acrylic glass for vertical light emission. It features optical, cone-like undercut microstructures for efficient illumination from a light guiding plate. This microstructured light guide is designed with the help of numerical raytracing simulations for the use as an innovative luminaire for room lighting. It can also find application in display technology for efficient backlight units. To realize such undercut microstructures in acrylic glass, a variothermal injection molding process, complemented by an ultraviolet radiation assisted thermal bonding procedure is introduced. By modifying the glass transition temperature of a thin surface layer of the microstructures the undercut microstructures can be bonded thermally to a light guiding plate without any glue or solvent, while the shape of the microstructures is perfectly preserved. Measurements verify the high bonding quality and confirm the good correspondence between measured light emission and ideal optical simulations.

Influence of polarization property of backlight unit on TFT-LCD transmission

Influence of polarization property of backlight unit on TFT-LCD transmission

Computational Super-Resolution Full-Parallax Three-Dimensional Light Field Display Based on Dual-Layer LCD Modulation

Due to physical limitation in resolution of display device, it is usually very difficult to achieve a high spatial resolution and a high angular resolution simultaneously for a three-dimensional (3D) light field display. Here, a computational super-resolution full-parallax 3D light field display is demonstrated, which can achieve both high spatial resolution and angular resolution. The proposed display consists of a specially designed backlight unit with controlled scattering angle, two cascadedly arranged LCDs with a resolution of 3840 × 2160, an aberration-suppressed compound lens array, and a holographic functional screen. The optical image formation processing of the display is analyzed and modeled as a whole process, and the superresolution light field synthesis method is presented. By co-designing the optical elements with computation processing, our proposed display architecture can improve the spatial resolution and angular resolution with a factor of 2× in both horizontal and vertical directions, comparing with these of the conventional light field display with single LCD and standard lens array. Finally, a super-resolution full-parallax 3D light field display with a designed spatial resolution of about 640 × 360 in a display area of 21.5 inches and an angular resolution of 166 × 166 in a viewing angle of 45 × 45 degrees is constructed, and an excellent 3D visual experience with improved image quality can be perceived.

75-inch LCD Displays with AM MiniLED Local Dimming Backlight Units on Glass

75-inch LCD Displays with AM MiniLED Local Dimming Backlight Units on Glass

75-inch LCD Displays with AM MiniLED Local Dimming Backlight Units on Glass

75-inch LCD Displays with AM MiniLED Local Dimming Backlight Units on Glass

Design and fabrication of submicron period grating as an imprinted light guide plate for a backlight unit

ABSTRACTThe imprinted light guide plate (LGP) fabricated through a diffractive grating was studied for the edge-lit display. Such kind of backlight unit (BLU) can save prismatic sheets. The grating dimension was determined through preliminary experiments, modeling, and computation. Based on the designed parameters, a submicron period grating was fabricated and was transferred to the LGP. Consequently, the outcoupling luminous flux, on-axis luminance, and homogeneousness and chromatic dispersion were measured through the prototyped samples. Compared to the conventional BLU, the imprinted diffractive grating works well as the light extractor but still needs to be improved to meet the illumination characteristics required for the liquid crystal display (LCD) BLU.

35.1: Invited Paper: Measurement and Standardization of Display Lighting Units

Display lighting unit has always been the focus for optimization when comes into display engineering to improve its electrical, optical, and electro‐optical performance. In recent years, with the development of reflective LCD (liquid crystal display), electronic paper display, laser projection display, etc., the measurement of display lighting unit has received more attention. The IEC TC110 "Electronic Display" established the standardization team PT62595 to develop international standards. Currently, the project team has worked a variety of lighting technologies, including back light unit (BLU) and front light unit (FLU), light module and engine, light bar, and light components. In this paper, we reviewed the roadmap of this group and key items that involve in the measurement methods to give an overview of the documents.In the previous year, the IEC released two new standards, IEC62595‐2‐2 “Measuring methods of LED light bars used in LCD BLUs” and IEC62595‐2‐3 “Electro‐optical measuring methods of LED frontlight unit”. Both documents have now been put into the implementation in the display industry.In IEC 6595‐2‐2, spatial luminance uniformity and angular luminance, color uniformity and color angular uniformity were addressed. In Figure 1, it shows an example of a typical light bar luminance distribution profile to indicate the luminance uniformity by quantifying the information along axis.Example of the luminance distribution profiles along the x‐axis, Lv(x, o)figureIn addition, in order to achieve these characteristics, the optical coupling analysis and optimization between the light bar and the light guide plate (LGP) was discussed. Furthermore, this work introduced the specifications on the requirements for test environment, the architecture of the test equipment, the reference diffuser settings, and the coordinate system.In IEC 62595‐2‐3, the standard specifies the measurement conditions and measuring methods for determining electrical, optical, and electro‐optical properties of LED FLUs for reflective displays. In FLU, the light ray of the FLU with a reflective LC display can be sensitive to the testing position and viewing direction. As shown in Figure 2, light rays are introduced to the LGP (light guide plate) from the coupling side. The rays are reflected on the inner surfaces of the micro‐structures (on the front surface) due to TIR (total internal reflection). The FLU is served as a transparent medium that has reflection property on both surfaces. We explained some of the factors that were covered in the standard document for the measurement and evaluation of both surfaces, including angular luminance distribution, luminance uniformity, spectral power distribution, chromaticity uniformity and angular color uniformity in CIE 1976 system, as well as FLU‐polarization characteristics and optical noise (undesired luminance) along the zenith angle in any azimuth angle.Light rays of FLU with a reflective LC displayfigure

P‐11.8: DCI‐P3 Representation by Using Nano‐IPS Technology

DCI‐P3 color space for digital movie projection is replacing Adobe RGB color space in Wide Color Gamut (WCG) monitor market. Nano‐IPS technology can achieve DCI‐P3 color space by using new advanced phosphors which can enlarge red and green color coordinates in LED backlight unit. This technology does not need to use WCG color filter panel, but need to use general high transmittance color filter panel.