Fabrication and evaluation of LED-embedded ribbons for highly flexible lighting applications in rooms

We have developed very flexible and lightweight LED-embedded ribbons in which LED-mounted printed circuit board (PCB) pieces are mounted and soldered to ribbons with the copper wires of power lines to apply them to the complicated three dimensional shapes of ceilings, walls, and furniture in rooms and provide higher levels of safety during earthquakes. Since it has been difficult to integrate LEDs in flexible ribbons and not only mount them on flat substrates but on bendable ribbons, we developed a new structure for LED-embedded ribbons and their fabrication process using a reel to reel mounting machine. A 2-cm wide ribbon with copper power lines on both sides was first constructed for the fabrication process of LED-mounted ribbons and then 5 × 20 mm LED mounted PCB pieces were mounted and soldered to the power lines of the ribbon. The ribbon was pulled under an optimal tension of 3.16 N to flatten the ribbon in the mounting process and the PCB pieces were pushed onto the ribbon with a rib height of 5 mm to strongly connect the pieces to the ribbon. The LED-embedded ribbon we constructed was 1.2 m long and very lightweight because it only weighed 7 g/m. The fabricated device had enough luminance of 96 lx for home and office lighting and could be installed on complicated surfaces such as adhering it to ceilings and the edges between ceilings and walls because our LED ribbon could be bent to a diameter of 5 mm. Our LED-embedded ribbon structure and assembly tool should provide new types of highly bendable and light-weight lighting for complicated three dimensional surfaces and safety during earthquakes.     

Development of reel-to-reel microchip mounting system for fabrication of meter-long LED lighting tapes

We have developed a reel-to-reel microchip mounting system that continuously mounts LED chips and other microchips on meter-long flexible printed circuit board (PCB) tape for 1.2-m-long standard LED light tubes. Mounting microchips on meter-long PCBs is difficult because a large chip mounter is expensive and the chip positioning stage is difficult to move in a meter-wide area with an accuracy of hundreds of micrometers. Hence, we developed a new microchip mounting system that utilizes a small chip mounter and reel winding machines. The system repeatedly moves the long PCB tape by a certain length with the reel winding machines and mounts the chips on it. The PCB tape (which is 5 mm wide) is made by fabricating long PCB tapes which are 25 cm × 26.6 m through a roll-to-roll PCB process and slitting them into meter-long tapes. The reel-to-reel system repeatedly mounts chips by adjusting their positions through image processing of the copper wiring pattern on the PCBs. Our constructed system mounted 24 LED chips with a pitch of 5 cm with an accuracy of 0.082 mm to form a 1.2-m-long LED tape. The luminance of the tape is 12.4 lx at a distance of 1 m, which is the luminance of outdoor corridor lighting. Therefore, this system can be used for meter-long tape lighting.     

Meter-scale large-area capacitive pressure sensors with fabric with stripe electrodes of conductive polymer-coated fibers

We developed meter-scale large-area capacitive fabric pressure sensors for floor sensors to monitor human position. In the fabric pressure sensor, two fabrics with stripe electrodes of conductive polymer-coated fibers woven into them were stacked vertically, and the capacitance changes between the top and bottom stripe electrodes were measured when pressure was applied. By using the die-coating of a conductive polymer and weaving the resultant fibers with meter-scale automatic looming machines, the 1 m × 1 m area with stripe electrodes at a 20 cm pitch was constructed. The pressure sensitivity, which depends on the number of the sensor fibers forming the stripe electrodes, was characterized and optimized to increase output capacitance change. The stripe electrodes with five sensor fibers were found to exhibit a capacitance change of 1.37 pF when pushed with the average foot pressure (i.e., 2.6 N/cm²), which is large enough to detect with conventional capacitance measurement circuits. Finally, pressure sensing with our woven pressure sensor fabric is demonstrated. Our meter-scale pressure sensor fabric technology will be used for bed and floor sensors for monitoring old people in nursing homes and hospitals.     

A design of high optical efficiency wedge type light guide plate adopting twin inclined cylindrical surface

We propose wedge type light guide plate (LGP) adopting twin inclined cylindrical surfaces (TICS) at the incident part of a LGP. It has higher optical efficiency than conventional wedge type LGP. In dimension of LGP which the thickness of incident part is 1.5 mm and that of luminance part is 0.7 mm, the optical efficiency of wedge type LGP adopting TICS is expected to be 96% in comparison with a normal flat LGP. In addition, there is an advantage to reduce the non‐uniformity of vicinity of light emitted diodes (LEDs) by TICS reflecting light laterally. However, it is necessary that the LED centers are aligned with the intersections of TICS. The misalignment of LED causes non‐uniformity of optical profile that is slightly larger than a normal LGP.     

经编机布匹瑕疵的在线视觉检测

为实现经编机织布过程中布匹瑕疵的实时检测,提出了一种基于机器视觉的实时检测方法。离线训练时分别学习有瑕疵和无瑕疵纹理布匹图像,自动求取纹理基元周期和纹理方向,用以构建实用的两方向Gabor滤波器组,进而提取有和无瑕疵图像特征。在线检测时,以离线所构建的Gabor滤波器组分解图像,以离线所求取的参数窗口化Gabor子图,进而提取子图特征并采用特征变化率来代替原始特征的方法以消除光照不均影响。实验表明,该方法可以适应不同纹理布匹检测需求,消除光照影响,布匹检测准确率高达99%,检测一帧（54 pixel×600 pixel）的平均时间为100 ms,实时性和准确性高,可实现经编机布匹瑕疵的在线实时检测。     

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.     

Multiscale construction and large-scale simulation of structural fabric undergoing ballistic impact

Certain classes of new lightweight structural fabric, primarily used for ballistic shielding, possess a multiscale structure constructed from microscale fibrils, which are bundled together to form yarn. The yarn are tightly woven into sheets. Since experimental ballistic tests for the evaluation, design and optimization of such materials are extremely expensive and time consuming, it is advantageous to develop models amenable to rapid computational methods. The purpose of the present work is to develop an efficient computational strategy in order to rapidly construct and numerically simulate multiscale representations of this class of materials. Large-scale simulations are presented to illustrate the potential of the approach in delivering realistic responses, involving dynamic penetration of a new lightweight structural fabric.     

Highly efficient large‐sized LED display with improved ergonomics

Abstract— We have proposed a new approach to engineering and manufacturing an indoor indicator based on energy‐effective super‐bright LEDs. In our design, the light from a small number of such LEDs was uniformly redistributed using a special light guide. Recently, we developed a multi‐segment (40) LED indicator with improved ergonomics and a luminance of up to 4000 cd/m². This indicator is also capable of displaying (apart from the digits) special symbols.     

Low level light therapy by Red–Green–Blue LEDs improves healing in an excision model of Sprague–Dawley rats

There are many methods of healing wounds. Among these, light therapy is reported to be beneficial, as beams assist the human body in treating, sterilizing, and regenerating cells. Both Laser and LED irradiation with specific wavelengths induce proliferation of fibroblasts depending on the wound area or wavelength and are effective in wound healing. This study used 8-week-old 250–300 g Male Sprague–Dawley Rats (ILAR Code: NTacSam:SD). The experiment was carried out for the non-irradiation group and the Red–Green–Blue LEDs irradiation groups (n of each group = 5). The experiment animals were relieved for 24 h after wounds had been excised and then the Red–Green–Blue LEDs irradiation groups were given irradiation therapy over 9 days 1 h per day. Immunohistochemical staining was conducted for cytokeratin in order to precisely measure the defect size. Also, Masson’s trichrome staining was conducted for comparison of collagen between the Red–Green–Blue LEDs irradiation groups and the non-irradiation group. Animals treated with Blue LEDs irradiation (p < 0.05), Green LEDs irradiation (p < 0.05), and Red LEDs irradiation (N.S.) healed at a faster rate than non-irradiated group. The LEDs irradiated groups also had more collagen, according to Masson’s trichrome staining for collagen analysis. The Red–Green–Blue LEDs irradiation had a beneficial effect on wound healing and could probably replace low power laser treatment.     

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.     

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.     

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%.     

Fabrication of cone-like microstructure using UV LIGA-like for light guide plate application

The microlens array is usually formed by thermal reflow of polymer disks and can be one microstructure of the light guide plate (LGP). Here, we propose an ultraviolet (UV) backside exposure technology to fabricate the photoresist cone-like microstructure on the PMMA substrate at room temperature and then use UV LIGA-like process to transfer the microstructure for the application of 3.6 in. (72 mm × 57.5 mm) LGP. The electroforming was used to transfer UV master mold to the inverse cone-like microstructure of nickel metal mold and then hot embossing was used for one more pattern transfer to the same cone-like microstructure on PMMA substrate. The optical microscope and alpha-stepper profiler were used to examine the morphology and profile of LGP microstructure. The optical luminance and uniformity of LGP were measured using BM9 luminance meter in comparison with commercial product. The light uniformity and luminance of the cone-like LGP microstructure reach 75–80% and 2,800–3,000 cd/cm², respectively which meet the requirements of commercial LGP.     

Advances in automotive interior lighting concerning new LED approach and optical performance

Automotive interior lighting has to follow general trends in lighting and will therefore evolve toward hundreds and even thousands of RGB LEDs per car. Creating mood at day and night, pixelated sign‐like information, and theater‐like effects like welcome and goodbye messages are examples for outstanding user experience. Furthermore, safety features such as warnings and driving state are a must for autonomous cars. It requires new concepts for the whole interior lighting system to reach premium quality such as data rate (beyond today's bus standard for lighting), support for safety rules, compensation of temperature effects, daylight performance (including huge dimming range for night drive), uniformity in terms of luminance and color along the light guide, and mixing of red, green, and blue (RGB) with white. We report a new automotive RGB light‐emitting diode (LED) system that fulfills the above requirements and saves effort as well as cost by calibration before integration. Extensive studies were performed for daylight threshold evaluation with subjects and methods for judging on uniformity for direct‐lit RGB light guides based on the contrast sensitivity function and Gaussian fit of the LED luminance profile.     

机织物材料的多尺度模型及其应用

采用机织物的正交各向异性本构模型模拟不出某些悬垂和屈曲现象。为此,引入机织物的多尺度力学模型,建立完整的适合于进行机织物悬垂屈曲模拟的数值分析方法模型,采用多尺度有限元方法模拟其在自重作用下的悬垂及屈曲。与以往采用的正交各向异性力学本构模型相比,多尺度力学模型更加客观地反映了机织物所特有的力学性能;与传统有限单元法相比,多尺度有限单元法的基函数具有能反映单元内参数变化的优点,因此,这种方法能在大尺度上抓住解的小尺度特征,获得较精确的解。采用8结点壳单元离散织物片,这种壳单元为大变形而设计,有能力描述织物片在悬垂中发生的大转动。采用多尺度力学模型的模拟结果显著提高了计算精度,与实验结果吻合较好。     

基于MSC Patran参数化建模的飞艇蒙皮织物面内刚度预测

为研究飞艇蒙皮PBO织物的编织单胞并优化编织方案,假设单胞为宏观均匀的复合材料,基于MSC Patran,借助PCL建立参数化2D平纹织物模型,并分析编织纤维间隙、编织纤维截面夹角和树脂层厚度等参数与面内刚度的关系.结果表明,降低编织纤维间隙、减小编织纤维截面夹角、减薄树脂层厚度,可以提高织物面内刚度. 该模型及其模块可以拓展MSC Patran的功能,所开发的程序可为该类材料的编织设计提供便捷的开发工具.     

Luminance enhancement without sacrificing the viewing angle in a direct-lit backlight by addressing the angle-dependent characteristic of the prism film

In a conventional backlight, suppression of light loss caused by the prism film(s) is desired to enhance the luminance without sacrificing the viewing angle. In this paper, in a direct-lit light-emitting diode (LED) backlight, where an LED array is placed under the display panel, the transmission efficiency against the prism film(s) is investigated for incident light with different zenith and azimuth incident angles. A strong angle-dependent characteristic is found, even when the reflective recycling effect is available. To address this angle-dependent characteristic in a direct-lit LED backlight, a freeform lens is designed to deflect the light emitted from an LED into the incident angle range with high transmission efficiency. Two design examples are implemented by adopting dual- and single-layer prism film(s). The simulation results show that the freeform lens can enhance the on-axis luminance by 26% and 35%, respectively, while the viewing angle remains nearly unchanged. Furthermore, using a single layer of prism film, a 19-in. direct-lit LED backlight module is constructed for experimental verification. By fabricating the freeform lenses and adding them to the backlight module, the on-axis luminance is enhanced by 24%, and the viewing angle is decreased by no more than 2°. Finally, the influence of the diffusers, which causes the experimental results to degrade slightly compared with the simulation results, is analyzed.     

Simulation of a high-power LED lamp for the evaluation and design of heat dissipation mechanisms

High-power LED lamps have been under intense development in recent years. However, issues related to heat dissipation on the LED chip continue to plague research efforts. Heat generation increases with the power of the LED chip and heat accumulation is exacerbated by the plastic casinge of the lamp. Accumulated heat can seriously shorten the lifespan of an LED device. Consequently, manufacturers are constantly seeking ways to improve heat dissipation via heat transfer mechanisms. Little analysis has been performed on coupling the fluid field and heat dissipation inside LED lamps. Using FLUENT software, this study developed a simulation method for LED lamps in order to investigate thermal and fluid fields inside a lamp. The simulation results of an 8 W LED lamp predicted a chip temperature of 75.1 °C and maximum air velocity of 97.3 mm/s within the lamp with two sets of air circulation. The proposed model facilitates new fin designs and the determination of the optimal inner-shell thickness with the proposed design of a LED lamp having 36 fins and an inner-shell thickness of 1 mm for increased heat dissipation.     

A complementary matching technique to reduce the variance of optical and electrical properties of light‐emitting diodes

Abstract— Light‐emitting diodes (LEDs) using phosphor conversion inherently have a wide variation of multiple parameters, including correlated color temperature (CCT), light output power (LOP), and forward voltage VF. A method, based on the formation of LED pairs with complementary characteristics, is presented to produce LED‐based light sources with narrow CCT, LOP, and VF distributions. A weighted matching algorithm was developed to select LED pairs under a multiple selection criteria. Based on the weighted matching algorithm, 96 LEDs were combined to form 48 LED pairs, and it was experimentally demonstrated that the variance of LED CCT and LOP distributions decreased by 93% and 71 %, respectively.     

A study on overhead glare in office lighting conditions

Abstract— High‐intensity light sources illuminating the human eye may create discomfort glare, or at higher intensities even disability glare. In many office lighting conditions, light from overhead luminaires in the ceiling may deliver stray light into human eyes, and as such create discomfort glare, generally referred to as overhead glare. In this paper, overhead glare for a LED luminaire comprising a matrix array of small LED sources using subjective evaluation methodologies and theoretical models, commonly accepted to evaluate glare, were investigated. The perceived overhead glare of the LED luminaire is evaluated at various luminance levels and at different angles (i.e., between 55 and 90°) with respect to the line of sight of the viewer. The results show that a luminaire comprising a matrix of high‐intensity point sources can cause overhead glare and can become glary at lower averaged luminance levels than a luminaire with a uniform light source even at high evaluation angles with respect to the line of sight of the viewer. In addition, the conventional UGR model for predicting discomfort glare needs adaptation for a reliable prediction of perceived overhead glare of complex LED luminaires consisting of a matrix of small‐sized high‐intensity light sources.