一种大功率低噪声的智能可调LED驱动设计方法

针对大型LED显示屏驱动中恒流源功率较小、调光不便捷,其开关特性导致的噪声大的问题,提出一种体积小,适用功率大且纹波效果较好的智能优化式恒流LED驱动设计方法。该设计在以往低电流的基础上进行改进,通过运放反馈调节将输出电流的开关特性转换为线性,辅以通断RCD回路(峰值吸收回路)和构建优化式大电流环式PCB布局,能进行光源检测的电流转脉宽式精准调光,输出能够较完善地抑制开关噪声。该设计方法能实现上位机网络远程数字调光,内、外部模拟调光,多路板载级联的智能控制。实验表明:该恒流驱动输出电流可达10A,功率可达370W,输出电流误差小于1%,驱动光源光功率稳定,光照分布均匀,具有较好的纹波效果,稳定可靠。     

基于IWC系统的功率型LED散热研究

针对功率型LED芯片现有散热方案的缺陷,设计了一种“针-网”式离子风散热（Ionic wind cooling,IWC）系统。并通过试验对不同曲率半径、分布密度的针电极结构以及不同电晕放电控制方式下IWC系统作用于功率型LED的散热性能进行了测试。采用红外热像仪测得了离子风对于发热体强化传热作用下的系统温度分布。结果表明：IWC系统的散热效果显著,针电极曲率半径为80 μm、针电极间距为7.5mm时,散热效果最佳;电晕功率为3W时,IWC系统能在较短时间内降低LED芯片引脚温度。     

LED照明产品的光生物安全测量的不确定度评定

为评定照明产品的光生物安全测量的可靠性,提高测量结果之间的可比性,依据JJF1059.1—2002《测量不确定度的评定和表示》和GB/T 20145—2006《灯和灯系统的光生物安全性》标准进行测量和评定,分析测试过程中的影响因素,建立数学模型,对LED照明产品的光生物安全测量进行不确定度评定。     

数字电位器DS3906在三基色LED显示屏中的应用

本文介绍了Dallas Sem iconductor最新推出的I2C总线数字电位器DS3906的引脚功能、内部结构、编程方法以及在LED显示屏控制中的应用和使用中的注意事项等。     

Improve uniformity for an indoor visible light communication system

Visible light communication (VLC) is an alternative technology to the radio frequency (RF) for different applications in the indoor and outdoor environments, it could be utilized for illumination and communication simultaneously, and it offers several advantages over contemporary RF technologies such as low power consumption, free license, large bandwidth, and being friendly to the environment. In this paper, an indoor VLC system uniformity improvement in terms of high received power, signal‐to‐noise ratio (SNR), and bit rate, with RMS delay spread reduction, is proposed. It features a novel model that utilizes a 13‐optical attocells configuration on the ceiling. Moreover, proposed model was evaluated at different semi‐angle at half power. The average received power and SNR were improved to 2.85 dBm and 75.5 dB, while achieved received power and SNR levels at the center of the room were 4.92 dBm and 79.5 dB, respectively. A minimum average RMS delay spread of 0.4749 nanoseconds is obtained, while the highest average bit rate calculated is 211 Mb/s. The proposed model provides a better communication quality and meets illumination standards requirements.     

Neuro-controller for broadcast lighting light-emitting diode to express white light with high color rendering index

Technical characteristics analysis related to correlated color temperature (CCT), color rendering, and illuminance is required to use light-emitting diode (LED) as broadcast lighting. In general, to realize a white light source with a high color rendering index (CRI), we selected the appropriate emission intensity of RGBW LED through trial and error. However, the characteristics of the LED light source and environmental conditions make it difficult to perform the procedure several times. The objective of this study was to design a system that could control illuminance, CCT, and ∆uv while having high CRI, as an LED control method for broadcasting lighting. The controller implements using a feed-forward neural network with excellent nonlinear function approximation capability. We measure data directly from the red green blue white (RGBW) LED system for neural network training. We then select data with high CRI from the measured raw data and choose data for neural network learning by removing measurement noise using the quadratic polynomial interpolation method. The performance evaluation confirms that the proposed neural network controller shows excellent results as an RGBW LED controller for broadcast lighting in the Planckian locus and all regions of white light.     

Mini LED背光源在液晶显示面板上的照度均匀性

基于Taguchi实验方法和Tracepro仿真软件,研究了 Mini LED背光模组中LED芯片大小、芯片发光半角、芯片出光面到液晶层的距离等因素,对液晶面板照度均匀性的影响规律并对其进行了相应分析.研究结果表明:芯片出光面到液晶层的距离对照度均匀性影响最大,影响因素的权重占比达到82.88％;发光半角占比14.33％:芯片大小占比为14.33％.根据研究结果,固定发光半角与芯片尺寸,调节出光面与液晶面板层的距离,得到了最优的照度均匀度.     

The effect of the illuminance of light emitting diode (LED) lamps on long-term memory

In this study, the effect of the illuminance of LED lamps on long term memory is verified in the conditions of 400 lx, 700 lx, 1000 lx according to the standards of study room illuminance between 400 lx, the minimum and 1000 lx, the maximum suggested by KSA 3011. Word fragment task is used to measure the long term memory. As a dependent task, 90 words made up of 7 letters are selected among 2700 words which have low frequency provided by sesame word. According to the experiment result, the rate of long term memory is 60.42% under the condition of 400 lx, which is the most effective, 59.38% under the condition of 700 lx, and 52.68% under 1000 lx. In addition, the p value between 400 lx and 1000 lx is 0.028, which is statistically significant. The significance of this study lies in that the effect of the illuminance of LED lamps on long term memory, rather than the existing issues such as attentiveness or work memory is searched, suggesting the possibility that the lower, rather than lighter the illuminance of LED light is, the more effective long term memory is.     

Influences of substituting Na+ ions in Eu2+, Mn2+ doped Ba9Y2Si6O24 phosphors

Near-ultraviolet (NUV)-excitable phosphors composed of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0–0.8) and Ba_8.7-qNa_0.4Eu_0.1Mn_qY₂Si₆O₂₄ (q = 0–0.4) were prepared via a solid-state reaction in a reducing atmosphere. The X-ray diffraction patterns of the obtained phosphors were examined to index the peak positions. After Na⁺ substitution for Ba²⁺ in the Ba_8.9Eu_0.1Y₂Si₆O₂₄ host lattice, the clear shift from green to yellow emission was observed. The Gaussian components of Ba_8.9-(1/2)pNa_pEu_0.1Y₂Si₆O₂₄ (p = 0, 0.4, and 0.8) phosphors were exploited by using the three different Eu²⁺ ion sites in the host lattice. The dependence of the luminescent intensity of the Mn²⁺ co-doped (q = 0–0.4) host lattices on the fixed Na⁺ and Eu²⁺ contents was also investigated. Co-doping Na⁺ with Mn²⁺ and Eu²⁺ emitters in the host structure enabled efficient energy transfer from Eu²⁺ to Mn²⁺. The mechanism underlying this energy transfer was also discussed. The Commission Internationale de I’Eclairage (CIE) coordinates near the yellow and red regions of the obtained phosphors were observed. Each of Ba_8.9Eu_0.1Y₂Si₆O₂₄, Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄, and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors with a 405 nm LED chip was fabricated. The color rendering index (CRI, R_a) at correlated color temperature (CCT) with the CIE coordinates was exhibited for the LEDs. The thermal quenching and activation energy for the Ba_8.7Na_0.4Eu_0.1Y₂Si₆O₂₄ and Ba_8.6Na_0.4Eu_0.1Mn_0.1Y₂Si₆O₂₄ phosphors were measured.     

Lighting assessment of ergonomic workstation for radio diagnostic reporting

Within the diagnostic process, in the activities in which digital radiology systems are utilised, image display devices play a very important role. Such devices have to guarantee high performances in order to maintain the diagnostic quality of the displayed images and present them so that they can be observed optimally. In order to ensure the appropriate performance to the users, not only the image display device but also the whole workstation should be designed properly. Particular attention should be paid to the lighting conditions, to avoid compromising the radiologist's ability to observe the displayed images.The aim of this study is to assess the lighting of some workstations used for diagnostic radiology reporting, in order to obtain information about the visual interaction between worker and device and prevent health risks. A detailed analysis of the lighting of adjustable and nonadjustable workstations used for diagnostic radiology reporting was carried out in different rooms of the Radiology Department at the “Felice Lotti” Hospital in Pontedera (Pisa, Italy). The analysis was carried out thanks to in situ measurements (objective analysis) and the submission of an evaluation questionnaire to a sample composed by 16 radiologists (subjective analysis).From the obtained results it has been possible to point out that, in nonadjustable workstations the absence of a dedicated lighting system very often reveals the inadequacy of the general lighting in guaranteeing correct lighting conditions for the radiologists during the reading of the diagnostic monitors. As measure to reduce the visual fatigue of the radiologists, the use of a supplementary adjustable innovative LED backlight system was proposed. The use of the LED backlight system allows complying the requirements of the Technical Standards and mitigate the difference of luminance in the field of view of the radiologist. Due to that the use of the LED backlight system has been positively perceived by the examined sample, a significant part of whom has ascribed to this use a reduction in the visual fatigue.