Development and application of less‐mercury flat fluorescent lamps for backlights and general lighting

Abstract— A novel flat discharge fluorescent lamp used as the light source of backlight modules for LCDs and general lighting systems has been researched and developed. This new type of lamp is a less‐mercury flat fluorescent lamp with two‐dimensional emission and superior to conventional one‐dimensional cold‐cathode fluorescent lamps in terms of optics, energy‐savings, production efficiency, reliability, and chromatic performances. Physical characterization of the optics, temperature, mechanical design, thermal shocking, reliability, and corresponding environments have verified that flat fluorescent lamps will be the next‐generation light sources for backlight modules and general lighting systems.     

Optical CMOS sensor system for detection of light sources

An integrated silicon colour measurement system has been designed for low-cost measurement of ambient light conditions, which can be used for adaptive control of displays in portable instruments, or for testing the intensity or colour temperature of light sources. The system is CMOS compatible and has a bitstream output. The response of two vertically stacked photodetectors with a different spectral response are sequentially available at the output. It is demonstrated that daylight can be clearly distinguished from several other light sources, such as incandescent lamps and fluorescent lamps.     

Wide‐angle film diffuser

Abstract— A unique roll‐to‐roll mass‐producible high‐transmission wide‐angle diffuser (WAD?) film for use in LCD backlights is reported. WAD? diffuser films include optical structures that efficiently manage forward light scattering and significantly reduces backward light scattering. WAD? technology facilitates backlights with significantly higher brightness and thinner backlight profiles.     

Predicting plasma properties using power‐controllable fluorescent lamps under electromagnetic wave radiation

This research proposed an experimental method to predict plasma properties in fluorescent lamps with the aid of electromagnetic (EM) wave propagation. A set of power‐controllable fluorescent lamps are placed between two antennas as a layered plasma medium. The electron density of plasma was adjusted through luminance control of the fluorescent lamps, and the transmission of the EM wave through the area occupied by plasma was achieved. The EM wave reflection and transmission through the plasma area were experimentally measured. By using the time‐domain experimental method, and with aid of the Fourier transformation, EM wave changes in the phase and variance in the intensity are tested. The plasma collision frequency and electron density are then mathematically derived based on the EM wave scattering model theory in unmagnetized plasma. This research provides an experimental approach to predict the plasma properties and diagnose the interaction between EM waves and plasma. The proposed experimental method can be implemented with other types of antennas and extended to a wide range of circumstances, such as monitoring the discharge changes in other plasma sources.     

Global relative parameter sensitivities of the feed-forward loops in genetic networks

It is well known that the feed-forward loops (FFLs) are typical network motifs in many real world biological networks. The structures, functions, as well as noise characteristics of FFLs have received increasing attention over the last decade. This paper aims to further investigate the global relative parameter sensitivities (GRPS) of FFLs in genetic networks modeled by Hill kinetics by introducing a simple novel approach. Our results indicate that: (i) for the coherent FFLs (CFFLs), the most abundant type 1 configuration (C1) is the most globally sensitive to system parameters, while for the incoherent FFLs (IFFLs), the most abundant type 1 configuration (I1) is the least globally sensitive to system parameters; (ii) the less noisy of a FFL configuration, the more globally sensitive of this circuit to its parameters; and (iii) the most abundant FFL configurations are often either the least sensitive (robust) to system parameters variation (IFFLs) or the least noisy (CFFLs). Therefore, the above results can well explain the reason why FFLs are network motifs and are selected by nature in evolution. Furthermore, the proposed GRPS approach sheds some light on the potential real world applications, such as the synthetic genetic circuits, predicting the effect of interventions in medicine and biotechnology, and so on.     

Flicker visibility and related visual discomfort in 3‐D displays with LED backlight

Abstract— In this paper, the perception of flicker in time‐sequential or field‐sequential 3‐D LC TVs driven by LED backlights is described. The seriousness of the perceived flicker and its influence on visual discomfort is investigated for various backlight operational modes. Results show that display backlights presenting different temporal light distribution have significant contribution to flicker visibility and visual discomfort. The display dimension, 2‐D or 3‐D, affects visual discomfort but not flicker visibility. The relationship between visual discomfort and flicker visibility is proportional when rendering 2‐D images, but not in the case of 3‐D images. Finally, a simple model is presented to evaluate visual discomfort related to flicker in 2‐D rendering.     

Thin‐film encapsulated white organic light top‐emitting diodes using a WO3/Ag/WO3 cathode to enhance light out‐coupling

An alternative design of a semitransparent cathode for top‐emission white‐fluorescent organic light‐emitting diodes (OLEDs) has been investigated. The scope of this study was to improve the luminance of OLEDs used for displays while keeping the current density versus voltage characteristic unchanged for addressing purposes. The use of an optical simulation tool allowed the optimization of the tri‐layer cathode WO₃/Ag/WO₃ to increase the light out‐coupling coefficient of the device leading to an increased white emission compared with a reference device with a Ca/Ag cathode. An increase of ~40% in luminance has been calculated by simulation and experimentally confirmed. The p‐i‐n OLED structure underneath the tri‐layer cathode allowed an efficient injection of electrons independently from the work function of WO₃. The WO₃/Ag/WO₃ cathode has been also confirmed to be compatible with the atomic layer deposition technique for thin film encapsulation. Finally, lifetime measurements up to 600 h have been carried out to quantify the enhancements induced by the new cathode compared with the control device. It has been found that lifetimes of both cathode architectures are similar on this time scale, while the WO₃/Ag/WO₃ cathode shows a lower voltage drift versus aging.     

Étendue‐density homogenization lamps with light concentration function

Abstract— In order to increase the screen brightness of Digital Micromirror Device? projectors (DMD? projectors), we designed a new compact lamp. In our previous work, we discussed a lamp that has an aspherical lamp reflector and an aspherical front glass, which we called EHLa. Although EHLas improve the light convergence at the entrance of rod integrators, they require external lenses for light condensation. We, therefore, discuss a new EHLa that can converge light without the need for external lenses. The new lamp corresponds to conventional elliptic reflector‐type lamps, which are widely used for mobile‐type DMD? projectors. Our simulations demonstrated that the ratio of increased brightness is 17.1% for the new lamp design versus conventional lamps in a 0.7‐in.‐diagonal DDR DMD? panel.     

Flexible inverted bottom‐emitting organic light‐emitting devices with a semi‐transparent metal‐assisted electron‐injection layer

Abstract— The development of highly efficient and color‐saturated green‐fluorescent C545T dye‐doped flexible inverted bottom‐emitting organic light‐emitting diode (IBOLED) is reported. This was enabled by the insertion of a silver (Ag) based semi‐transparent metal‐assisted electron‐injection layer between the ITO cathode and n‐doped electron‐transporting layer on a flexible polyethersulphone substrate. This flexible IBOLED with an ITO/Ag bilayer cathode with its synergistic microcavity effect achieved luminous efficiencies of 20.4 cd/A and 12 lm/W and a saturated CIE^x,y of (0.28, 0.68) at 20 mA/cm², which are 1.5 times higher than those of a conventional OLED.     

Thermal‐deformation characterization on the panel of TFT‐LCD TV. Part I: Mechanism of color distortion

Abstract— In this study we applied both numerical simulation and experimental validation to characterize the thermal deformation of the panel and the direct‐lit backlight unit (BLU) of a thin‐film‐transistor liquid‐crystal‐display television (TFT‐LCD TV). Heat emitted from cold‐cathode fluorescent lamps (CCFLs) causes thermal deformation of the LCD and extrudes the panel from the metal front shield at both upper corners: this finally leads to color distortion. In the numerical simulation based on thermal‐fluidic fields of the TFT‐LCD TV, natural convection of air that surrounded the CCFLs resulted in a high temperature at the upper‐right and upper‐left corners of the LCD panel. Numerical results were verified by temperature measurements with good consistency. Additionally, this study has established a measurement system to characterize the temperature distribution on both the BLU and panel and the thermal deformation of the panel causing the color distortion.     

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.     

Diffractive backlight grating array for mobile displays

Abstract— The display backlight unit (BLU) is the most power‐consuming subunit in mobile liquid‐crystal displays. The state‐of‐the‐art BLUs utilize scattering, refractive, and reflective microstructures to generate a uniform distribution of white light through the display. More effective means of transmitting light through the display color filters could be obtained by using diffraction, but previously proposed diffractive backlights do not fully utilize all the possibilities to design gratings effectively for optimal color separation and outcoupling. This paper presents a new pixelated diffractive backlight grating array as an approach for overcoming these obstacles in BLU design. A model array was fabricated to couple out red, green, and blue primary colors from the respective subpixel locations. The results show that it is possible to manufacture such an array and that the light couples out as intended, giving a starting point to design mobile‐display modules with low light‐transmission losses.     

LED backlighting for LCD HDTV

Light‐emitting diodes (LEDs) are used today for backlighting of small displays such as PDAs and mobile phones. We show in this paper that a new LED technology can be used for high‐demanding display‐backlighting applications such as LCD HDTV. Using this new type of emitter, called a Luxeon? Power Light Source, a brightness higher than an edge‐lit CCFL backlight can be achieved, while compared to a direct‐lit CCFL backlight the thickness is lower and the uniformity is better. With on‐going improvements in LED performance over the coming years, LED backlights will reach and even outperform the brightness performance of direct‐lit backlights while maintaining the benefits of edge‐lit solutions at even higher brightness levels.     

Diffraction on birefringent elements with sine surface microrelief

Abstract— Light diffraction on optically anisotropic substrates using sine surface microrelief has been calculated by using the OAGSM method. The influence of the microrelief depth and material birefringence on the diffraction intensity on the order of 0–3 is reviewed and discussed. The results are compared with the results of the calculation for a rectangular microrelief. The microrelief depth and material birefringence allows the realization of different polarization states of the light beam transmitted or reflected by the substrate. The approach can be used to control the light‐beam propagation for different applications including LCD backlights.     

Physical‐based photon mapping for an LED backlight lighting simulator

Abstract— Liquid‐crystal displays (LCDs) have become increasingly popular due to their lower price and larger sizes. In particular, backlights having an RGB LED source have recently attracted attention, because they have a wider color gamut, higher luminance, and lower power consumption. However, even when the backlight area is uniformly covered with light modules based on arrays of individual LEDs, this does not ensure a uniform chromaticity and luminance over the backlight panel, thereby stressing the need for lighting simulation of the backlight. Accordingly, this paper proposes an effective lighting simulator to predict the chromaticity and luminance distribution of an LED backlight panel for an LCD. First, the spectrum‐based photons are all initially generated using a random function with a constraint satisfying the spectral power distribution of the actual LED light sources, while their emitting directions are determined based on a pre‐calculated probability using a random variable angle. The optical characteristics of the inner sheets in the LCD backlight structure are then modeled using the wavelength and incident angle to predict the next direction of each photon based on the reflection and transmittance at an intersection. All the photons that reach the unit area of the outward panel are gathered to shape their spectral power distribution, then converted to CIEXYZ values and multiplied with a color‐matching function. Finally, a realistic image visualization of these CIEXYZ values is achieved through standardized device characterization using the sRGB mode. Experiments confirm that the proposed spectrum‐based photon mapping can effectively predict the chromaticity and luminance distribution of an LED backlight panel, providing a good lighting simulation of an LED backlight before manufacturing the LCD.     

Sphere‐supported thin‐film electroluminescence: A new platform technology for displays and lighting

Abstract— Currently, powder electroluminescence is used for low‐brightness flexible lamps offering durable plastic‐based lighting solutions principally for low‐ambient light conditions where lighting or backlighting is required. Sphere‐supported thin‐film electroluminescence (SSTFEL) promises dramatic new capability in both flexible lamps and displays owing to its high brightness and long‐life capability. SSTFEL is based on robust thin‐film phosphors deposited on spherical ceramic dielectric particles which are embedded in a thin plastic sheet. A printing approach permits versatile, low‐cost manufacturing of patterned SSTFEL devices and eliminates the need for high‐temperature substrates.     

Locally pixel‐compensated backlight dimming on LED‐backlit LCD TV

Abstract— The pixel brightness of an LCD panel perceived by a user is the product of the backlight brightness and the panel transmittance. In conventional LCD panels, the backlight brightness is constant and always at peak luminance. This design suffers from light leakage and power waste problems at dark scenes. This paper presents a new LCD system, which uses locally pixel‐compensated backlight dimming (PCBD). The proposed method combines backlight control and pixel processing for reducing light leakage and power consumption while keeping the image at the original brightness. Backlight luminance is dimmed locally in the dark‐image region, and pixel values are compensated synchronously according to the luminance profile of dimmed backlight. By reducing the light leakage, a static contrast of over 20,000:1 has been achieved on a large‐sized LCD panel with the proposed PCBD method. No obvious artifacts have been noticed as well. The power consumption of the panel can also be greatly reduced, depending on various video content. The PCBD method could be widely used for developing state‐of‐the‐art LCD panels with LED backlights.     

LCD backlights: with or without Hg?

High luminance and efficacy vs. temperature independence and environmental protection: these are the determining factors for the choice of Hg or Xe for LCD backlights. A capacity‐coupled cylindrical Hg discharge lamp attains a luminance of 114,000 cd/m² and an efficacy of 35 lm/W when driven at 5 MHz. On the other hand, a mercury‐free Xe flat discharge backlight produces 11,000 cd/m² and 30 lm/W, with fast luminance response. This paper discusses the underlying limitations assessed to the Hg and Xe backlights, considering application to LC TVs.     

Ubiquitous interaction with positioning and navigation using a novel light sensor-based information transmission system

This paper describes a novel light sensor-based information transmission system for indoor positioning and navigation with particular benefits for mobile and wearable computers. It can seamlessly extend outdoor GPS tracking to the indoor environment. In a novel manner, fluorescent light is used as the medium to transmit information, which is encoded by using a pulse-frequency modulation technique. The user receives the encoded light information through a photo-receiver. The information is passed into the wearable or mobile computer after the data is decoded. This information allows positioning information to be given to indoor mobile and wearable computers. We design an economical transmitter circuit by adding few components to a commercial electronic ballast circuit for fluorescent lamps with price of less than US $10. The propose system can be used in indoor guidance and navigation applications. Exemplary applications are included in the paper, with experimented results detailed.