Thermal consideration in LED array design for LCD backlight unit applications

This paper proposes high performance control of light emitting diode(LED) drive system for liquid crystal display(LCD) backlight. The CCFL(cold cathode fluorescent lamp)was used to a conventional LCD backlight. Due to improvement on luminous efficiency, long life and wide color gamut, LED has gradually substituted for CCFL as backlight. The backlight using LED is necessary to use many LED. For that reason, the LED backlight is using a lot of LED driving circuits. The many LED driving circuit is generated a current deviation between LED. Eventually, it is caused brightness deviation between LED. Therefore, this paper improves the current deviation using transformer and balancing capacitor to solve this problem. Also, for accurate and uniform brightnesss control, this paper is applied the artificial intelligent control to a dimming control. This paper is compared with conventional system, and validity of this paper proves through that result.

This work presents a detailed study about the heat dissipation performance of direct illumination high-power light emitting diode (LED) backlight units with two different assembling structures, one of which is traditional and the other is new. The traditional structure, referred to by structure-1, consists of multiple LEDs being directly welded to the printed circuit board (PCB), where the PCB is used as a physical support, an electrical connector and also as a heat dissipation medium. The new structure, referred to by structure-2, places the LEDs directly on the cooling boss; in this case the PCB plays mainly the role of an electrical connector. Thermal characteristics related to the two backlight units are analyzed in terms of thermal resistance network, numerically simulated and experimentally tested. The obtained results by different methods accord with each other reasonably well and all indicate that both structures can meet the requirements of heat dissipation for backlight units at an ambient temperature of 30 °C. Among the two structures, the LED junction temperature of structure-1 backlight unit is 7–8 °C higher and the temperature distribution in the back plane of the backlight unit is also more uniform.

In this paper, we evaluated quantitative changes in the luminance and the color on the light-exit plane of an LED edge-lit backlight unit (BLU) by systematically controlling the optical properties of individual white LEDs. We placed a light absorbing film and red-green-blue filters to control the white intensity and the color of an individual LED string, respectively. Impacts of this ‘defect’ LED's optical properties were systematically monitored across the light-exit plane in terms of local distribution of the luminance and the color, overlaying prism films and diffusion film on a light guiding plate (LGP). The roles of prism films and diffusion film were also experimentally analyzed to assess their homogenizing capability for the luminance and the color with respect to the defect-like LEDs.

As a typical computational method, Fourier ptychographic microscopy (FPM) can realize high spatial resolution and quantitative phase imaging while preserving the large field of view with a low numerical aperture (NA) objective. A programmable light-emitting diode (LED) array is used as a typical illuminator in an FPM system, and the illumination parameters of each LED element are crucial to the success of the FPM reconstruction algorithm. Compared with LED arrays arranged in rectangular arrays, LED arrays with special structures such as domes or rings can effectively improve FPM imaging results and imaging efficiency. As a trade-off, their calibration difficulty is greatly increased due to the lack of geometric constraints of rectangular arrays. In this paper, we propose an effective hybrid full-pose parameter calibration method for freeform LED array illuminators, combining stereoscopic 3D imaging techniques and the geometric constraints of the microscopic platform. First, a stereovision system is used to obtain the accurate 3D position of each LED element of the freeform illuminator and to construct a rigid 3D coordinate LED array system. Then, calibration between the coordinate system of the LED array and that of the optical imaging component is realized according to the geometric features of the brightfield-to-darkfield edges. Finally, we verify the feasibility and effectiveness of the proposed method through full-pose parameter calibration of LED arrays with different arrangement rules.

Large LED (light emitting diode) array lights are currently being designed and sold as replacements for lights on roadways, tunnels, parking lots and other large areas. These lights are typically 75 W to 200 W in thermal dissipation, and the lighting structure is designed to handle a predominately conductive heat path until contact with the outer air is made. At this point convection to the ambient air removes the heat from the system. To handle this internal conduction path to a suitable area for convection, most LED array lights have been developed using an aluminum heat sink, which causes a weight problem and additional costs over conventional light systems which are manufactured with sheet metal. Conventional sheet metal designs are deficient in providing an adequate thermal path for the LED thermal dissipation. A proposed solution is given in this paper with a sheet metal design enhanced for thermal conduction with flexible graphite. Eliminating the typical LED heat sink, it is shown that a sheet metal and graphite system can effectively cool the same thermal load. To prove this, an off-the-shelf LED street light was purchased, tested as a baseline, and then modified with the sheet metal and graphite design. Initial design work was performed with an analytical model, and then a prototype created from this design and shown to be of similar performance to the baseline - a system thermal resistance of 3°C/W from the PCB to the ambient, and a savings of 0.9 kg. A detailed CFD was also performed to evaluate the performance of the system and suggest possible improvements in air flow paths. Comparisons of the experimental and numerical results are given showing agreement in most areas.

Monochromatic light emitting diodes (LEDs) are getting more attention day by day for a very wide range of applications such as general lighting, signage, automotive lighting, display, water purification, and skin imaging. While they are taking place in a large number of applications, thermal challenges associated with the operation of LEDs have become a significant issue to address since their performance is greatly affected by thermal conditions. Thus, this study focuses on identifying thermal, optical, and electrical characteristics of an AlGaInP-based red LED considering the impact of the LED dome on the chip performance. The junction temperature measurement results obtained with forward voltage change method were validated with thermal imaging method (TIM) and computational models. It was observed that the LED dome may critically affect the thermal, optical, and electrical behaviors of the LED chip. In fact, a 3.7% increase in junction temperature and a 6.1% drop in optical conversion efficiency were found at the normal operation of the red LED after the LED dome was removed. The results were also compared with a blue LED, and lower junction temperatures were measured for the red LED at each driving current. The difference in junction temperature became even more noticeable at higher driving currents. Results have shown a good agreement between three different methods with a maximum variation of 6.9%.

Backlight unit (BLU) is one of essential components constituting liquid crystal display (LCD). It can be fabricated with several different methods. Cold cathode fluorescent lamp (CCFL) can be made with a low cost process and has high quality of color reproducibility. But it cannot provide a high quality of brightness & contrast and can raise environmental issue since Hg is used as a law material. White light-emitting diode (WLED) has long lifetime and dynamic control feature, but it has complicated structure and needs high fabrication cost. Meanwhile, carbon nanotube based BLU (CNT-BLU) enables local dimming and impulse & scan driving, and can accomplish best quality of moving pictures by maximizing brightness & contrast functions. However, high fabrication cost is a large barrier for commercialization. In this study, we applied low-cost electroless deposition process of the metallization comprising CNT-BLU substrate. Current fabrication processes of CNT-BLU go through several times of photo patterning and firing of CNT paste, which results in complicated and high-cost processes. Metallization of backlight unit can be made either with Cr (Mo) patterning using conventional photo process or with stencil printing of Ag paste. The former uses vacuum processes using expensive semiconductor equipments such as sputter and evaporator, and the latter uses expensive law material like Ag. BLU substrates are formed by firing and activating the CNT pastes which was printed on the metallizations. Fabrication of BLU substrate can be simplified with electroless deposition method and the cost can also be much lowered. In the present study, feasibility of electroless metallization on the CNT-BLU substrate was tested. Glass substrate was pretreated with base solution and then etched with buffered oxide etch (BOE) solution, followed by seeding process by alternating dipping the substrate in Sn and Pd solution in turn. Electroless Ni(P) deposition was conducted on the substrate using a commercial Ni(P) bath with varying P content (4–9wt%). Adhesion test was conducted with as-plated and fired specimens. The Ni(P) film with low P content showed better adhesion performance than those with high P content. Electrical conductivity was also high in the low P containing specimens. Sheet resistances of them, measured by four point probe, were several ohm/sq and it decreased one order of magnitude lower after firing at 460°C. Decrease of resistance results from phase transformation of metastable Ni(P) film into stable Ni & Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> P phase. Surface roughness of the substrate was ∼90nm after BOE etching and ∼200nm after Ni(P) deposition with 2µm thickness.

In this paper, a novel method is introduced to enhance the performance of vehicle-to-vehicle (V2V) visible light communication (VLC) by employing different transmitter (Tx) light-emitting diode (LED) array arrangements with different LED orientations. Improving the signal-to-noise ratio (SNR) is crucial for V2V VLC systems to provide long communication ranges. For this purpose, six transmitter configurations are proposed: single-LED transmitters, as well as 3 × 3 square-, single hexagonal-, octagonal-, 5 × 5 square-, and honeycomb hexagonal-shaped LED arrays. Indoor VLC studies using LED arrays offer a uniform SNR, while outdoor studies focus on optimizing the receiver side to enhance system performance. This paper optimizes system performance by increasing the SNR and communication range of V2V VLC systems by changing the geometry of the Tx LED array and LED orientations. A V2V VLC system using on–off keying (OOK) is modeled in MATLAB, and the SNR and bit error rate (BER) are simulated for different Tx configurations. Our results show that the honeycomb hexagonal transmitter design provides a 19% improvement in system performance with a spacing of 1 cm, and maintains a 16% improvement when the array size is reduced by a factor of 100, making it smaller than one of the smallest industrial headlight modules.

This paper presents the optimal design of the light-emitting diode (LED) array combinations for three typical nonisolated continuous-conduction mode single-loop control LED drivers. Based on the LED Taylor series model and the equivalent circuits of these three LED drivers, the quality factor functions in their transfer functions of the control-to-output current are derived to predict the optimal combination of the LED arrays according to the given circuit and LED parameters to fulfill the requirement of critical damping and maximum efficiency power conversion, which happen at unity quality factor. The three prototype circuits of three LED drivers with 120 LEDs are presented to verify the optimal design of the corresponding LED array combinations through the theoretical, simulation, and experimental results.

With a long experience in optoelectronics, CEA-LETI has focused on Light Emitting Diode (LED) lighting since 2006. Today, all the technical challenges in the implementation of GaN LED based solid state lighting (SSL) are addressed at CEA-LETI who is now an RandD player throughout the entire value chain of LED lighting. The SSL Line at CEA-LETI first deals with the simulation of the active structures and LED devices. Then the growth is addressed in particular 2D growth on 200 mm silicon substrates. Then, technological steps are developed for the fabrication of LED dies with innovative architectures. For instance, Versatile LED Array Devices are currently being developed with a dedicated μLED technology. The objective in this case is to achieve monolithical LED arrays reported and interconnected through a silicon submount. In addition to the required bonding and 3D integration technologies, new solutions for LED chip packaging, thermal management of LED lamps and luminaires are also addressed. LETI is also active in Smart Lighting concepts which offer the possibility of new application fields for SSL technologies. An example is the recent development at CEA LETI of Visible Light Communication Technology also called LiFi. With this technology, we demonstrated a transmission rate up to 10 Mb/s and real time HD-Video transmission.

This study evaluates the implementation and performance of a Visible Light Communication (VLC) system designed to transmit text data between two personal computers (PCs). The proposed system utilizes three distinct light-emitting diode (LED) —Single LED, 2 × 2 LED Array, and 4 × 4 LED Array—as transmitters and three types of photodetectors—BPW34 photodiode, solar cell, and light-dependent resistor (LDR)—as receivers. Controlled by an Arduino, the system investigates the relationships between data rate, transmission distance, beam angle, LED configurations, and detector types. Experimental results confirmed that the BPW34 photodiode outperformed the solar cell and LDR in terms of maximum achievable data rate and transmission distance, consistent with its superior bandwidth and sensitivity characteristics. The findings also reveal that, at a zero-degree beam angle, the system employing the BPW34 photodiode achieved a maximum transmission distance of 9.15 m at 1 kilobit per second (kbps) with a single LED configuration, diminishing to 1.24 m at 4 kbps. The 2 × 2 LED array extended the distance 14.20 m at 1 kbps and 2.30 m at 4 kbps. Conversely, the 4 × 4 LED array exhibited the most extensive propagation distances, achieving 16.30 m at 1 kbps and maintaining 3.25 m at 4 kbps. These findings underscore the efficacy of increasing LED array size in enhancing propagation distance, particularly at lower data rates. The study highlights the potential of VLC systems for efficient indoor optical communication, providing valuable insights for optimizing LED configurations and receiver technologies in future applications.

Estimating the economic life of a technology is the first important prerequisite step in the feasibility analysis of technology-based business. Many empirical studies have concentrated on patents data to estimate the time period for a technology. However, it is recommended to estimate it along with qualitative considerations of future technological and market conditions. In this regard, little is known about how approaches are applied. This paper aims to establish a structural framework of estimating the lifetime of a technology by integrating the outputs of an analysis of the determinants in each transition of a product life cycle. We describe an illustrative case about a light emitting diode (LED) backlight unit (BLU) technology for the liquid crystal display (LCD) TV. The framework allows valuators and experts to estimate a technology lifetime by using multidimensional factors.

This paper presents the optimal combination design of the light-emitting diode (LED) array for the single-loop continuous-conduction-mode (CCM) buck-boost LED driver. Based on the Taylor series to describe the LED exponential function, the dc and small-signal transfer functions of LED arrays are derived for the system analysis of the employed single-loop CCM buck-boost LED driver. In this paper, the derived system transfer functions of the employed LED driver are verified with SIMPLIS <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> simulation results. The combination design of a 120-piece LED array for the employed LED driver to have power conversion with optimal efficiency is obtained and validated through the theoretical, simulation, and experimental results.

A novel hybrid light guide plate (LGP) for large area light emitting diode (LED) display was proposed by combining the advantages of both direct- and edge-type backlight units (BLUs). The newly proposed hybrid LGP consists of a thin plate with specially designed aspheric concave structure on the top surface and semispherical micropatterns on both the top and bottom surfaces to enhance light uniformity and decrease color variation. The optical characteristics were investigated to realize the optimized geometry for improving the optical efficiency and uniformity. Ray-tracing simulation results for the 55 in. display show that the illuminance uniformity, optical efficiency, and color coordinate deviation are more than 96%, 81.5%, and less than ±0.004, respectively. In addition, this hybrid LGP has an advantage of thinner thickness and less number of LEDs over the commercial direct-type LGP as well as a much lower color variation over the edge-type LGP.

이 논문에서는 LED(Light Emitting Diode) 조명을 이용한 간편한 가시광 통신 시스템을 구현하기 위해, 비 캐리어 NRZ-OOK(non-return to zero on off keying) 변조 방식을 사용하고, 가시광 송신을 위한 발광소자인 <TEX>$3{\times}3$</TEX> 백색 LED 배열과 가시광 수신을 위한 여러 가지 포토다이오드를 사용하여 송수신 소자사이의 거리가 약 2.5m이고, 전체 시스템 속도가 115.2kbps의 전송속도를 가지는 가시광 시스템을 설계하여 구현 한다. 구현된 시스템의 성능분석을 위해 LED 와 포토다이오드 종류, LED 배열 수, 전송속도 따른 최대 송수신 거리를 구하고 여러 가지 구현시스템의 성능을 실험을 통해 분석한다. In this paper, as a study of the simple visible light communication(VLC) with LED light, the visible light communication system that are made up with the <TEX>$3{\times}3$</TEX> white LED array for visible light transmission, various photodiodes for visible light reception, and a non-carrier NRZ-OOK modulation scheme is designed and implemented to have a 115.2 kbps data speed at 2.5 m distance between transmitter and receiver. For the performance analysis of the developed VLC system, the maximum distance between VLC transmitter and receiver on the conditions of various transmission speeds, the number of LED array, or the various kind of LED and photodiode is obtained, and various performances are analyzed by experiments.