不同驱动模式下白光LED光色电性能分析

采用脉冲和直流两种驱动模式分别驱动同一批次的白光LED灯珠,对比分析了在"视觉亮度"一致时两种情况下的光色电性能,并研究了人眼视觉惰性对白光LED性能的影响。研究发现,在低脉冲占空比下,脉冲驱动LED的电流和发光效率比直流驱动的低,并且随着占空比的增加,两者的差值逐渐减小并趋于相等;当脉冲占空比高于70%时,两者驱动电流的差值增加,而脉冲驱动的发光效率却高于直流驱动的发光效率。此外,相比直流驱动,高脉冲电流驱动下的LED的发光更接近等能白光,进而增强了人眼对LED发光亮度的刺激响应,有效地提高了人眼的"视觉亮度"。     

不同驱动模式下白光LED光色电性能分析

采用脉冲和直流两种驱动模式分别驱动同一批次的白光LED灯珠,对比分析了在“视觉亮度”一致时两种情况下的光色电性能,并研究了人眼视觉惰性对白光LED的性能的影响。研究发现：在低脉冲占空比下,脉冲驱动LED的电流和发光效率比直流驱动的低,并且随着占空比的增加,二者的差值逐渐减小并趋于相等;当脉冲占空比高于70%时,二者驱动电流的差值增加,而脉冲驱动的发光效率却高于直流驱动的发光效率。此外,相比直流驱动,高脉冲电流驱动下的LED的发光更接近等能白光,进而增强了人眼对LED发光亮度的刺激响应,有效的提高了人眼的“视觉亮度”。     

大动态范围闪烁晶体荧光模拟器的设计

针对暗物质粒子探测卫星(DMPES)锗酸铋(BGO)量能器探测单元的标定需要,设计了一种用发光二极管(LED)作为光源的闪烁晶体荧光模拟器。首先,利用光电倍增管(PMT)测量BGO晶体在宇宙线辐射下的荧光脉冲,对脉冲波形建模拟合,并将波形存储到可编程信号发生器中。然后,选择一种峰值波长与BGO晶体的荧光发射波长相近,且其光通量与工作电流的线性度较好的LED,设计LED驱动电路,令LED的工作电流与模拟器输入的模拟电压信号幅度成正比。最后,利用信号发生器输出模拟的BGO晶体荧光脉冲波形至驱动电路,使LED发光,并利用积分球将LED的荧光通过光纤均匀地输出到多个PMT。实验结果表明:模拟器光脉冲测试结果与对BGO晶体实际测试的结果相似,光强覆盖PMT的2,5,8个打拿极(Dynode)输出,动态范围达4.11×103倍,满足暗物质粒子探测卫星BGO量能器地面检测系统的需求。该荧光模拟器也可用于同类闪烁晶体探测器系统的检测和标定。     

一种采用LED光源的光电效应测普朗克常数实验装置

针对目前利用光电效应测定普朗克常数的实验装置的不足,提出一种采用LED光源的实验装置。该装置采用谐振腔发光二极管(RCLED)作为单色光源,该光源单色性好,波长稳定,寿命长,驱动简单,不需预热,采用脉冲宽度调制(PWM)方式调节亮度准确方便,从而可以方便准确地验证光电效应实验规律及测定普朗克常数。测试结果表明:本实验装置测得数据比目前实验室采用高压汞灯作为光源的实验装置测得数据更准确。     

光源布置对汽车背景光系统亮度一致性的影响研究

汽车仪表中的光源布置决定着光源光照度分布从而最终影响汽车背景光的亮度一致性.本文讨论了汽车背景光发展现状及新型光源:发光二极管(LED)作为背景光源的应用情况,分析了目前LED在汽车背景光应用中存在亮度不一致的情况,着重研究了光源布置对汽车背景光亮度一致性的影响,提出了一种通过优化光源布置中相邻LED间距提高汽车背景光亮度一致性的方法.该方法在保证视觉亮度一致性的情况下充分利用了LED的光效,优化了LED的使用数量.实际汽车背景光部件设计中的成功应用证明了该方法的有效性.     

跑道关闭时机场标识灯自适应控制系统设计

在民用机场的跑道因施工等原因需要关闭时,需要一种高亮度的指示灯光来指示客机降落到其他跑道,要求飞行员在1.2km甚至更远距离就发现指示灯,以提前采取变道措施,并且要求指示灯亮度要与周围光强相协调,以防刺激飞行员的视觉而影响降落.基于此目的,本文介绍一种基于单片机的可实时根据外界光强调整指示灯亮度的系统,主要包括:太阳能充电系统,电源管理模块,光强采集模块,光强信息处理模块,灯光控制模块.本系统采用了目前脉冲宽度调制(PWM)措施来调节LED灯的亮度,既节能又保证了LED指示灯的使用寿命.     

LED线阵旋转控制系统的设计

采用LM3S2965作为控制芯片,通过16个LED组成LED线阵旋转平台,电机带动旋转平台,利用人的视觉延迟特性,可以在旋转平面上显示不同的图文。该系统能实现LED灯的依次自检、同心圆的大小交替变化、文字显示、指针秒表显示等功能,同时能根据环境亮度来调整LED的亮度。     

基于ARM和FPGA的LED标准光源电路设计

为满足光源亮度和准确度的要求,设计了一种能够调节光源亮度和色温的LED驱动电路,提出了一种基于ARM和FPGA的双芯片控制的LED驱动电路。采用ARM Cortex-M3内核的LPC1517作为主控芯片,负责数据的存储和处理,保证整体系统高速稳定运行;FPGA芯片EP1C3T144CN则负责输出LED工作所需的PWM信号,使得LED光源能达到所需色温。实验结果表明,设计的LED光源在亮度达到要求的前提下,实际色温与实验设定色温误差在1%以内,该LED光源发光性能良好,且体积较小、成本低,能应用于较多工作场景。     

基于WiFi调光的LED驱动控制器的设计

设计一种基于WiFi短距离无线数字通信技术控制LED光源亮度的驱动控制器。采用PWM控制LED光源亮度,用脉宽调制技术精确控制流过LED光源的电流,为LED光源提供恒定的驱动电流和安全稳定的负载。使用者可以通过手机控制软件设置四路LED光源的亮度、色温等光学参数,也可以根据相应的应用场合设置光照时间以及光照模式等。实验证明,该控制方法简易、可靠、方便,具有一定的实用意义。     

用彩色CCD相机测量发光二极管显示屏的色度

提出了一种高精度色度计和彩色CCD相机相结合快速测量发光二极管(LED)显示像素的亮度和色度的方法.首先,用彩色CCD相机测量LED显示像素,通过图像处理提取每个LED显示像素点在RGB颜色空间中的亮度值和色度值.然后,建立RGB颜色空间和CIE 19 31XYZ颜色空间的多通道自适应矩阵,并使用色度计对部分LED显示像素点进行精确测量,基于精确测量值和对应的RGB值计算出自适应矩阵.最后,通过自适应矩阵计算出所有LED显示像素的亮度和色度值.实验结果表明:自适应矩阵大小合适的情况下,该方法计算出的数据与色度计测量数据之间的色差值△E＜1,在人眼视觉中的颜色差异轻微,可快速、精确地采集LED显示像素的亮度和色度值,实现LED显示屏的高精度亮度、色度校正,从而大幅提高LED显示屏的显示效果.     

A new switched-capacitor frequency modulated driver for light emitting diodes

A new type of drivers for light emitting diodes (LEDs) is introduced based on the switched-capacitor frequency modulation. In contrast to conventional constant dc current drivers, the current pulse is provided by this new switched-capacitor LED driver. In the present driver, the charging capacitor is charged and discharged through a LED and the current flow direction is controlled by a metal oxide semiconductor switch. The input current (and thus the LED brightness) is proportional to the switch clock frequency at relatively low frequencies and becomes saturated at relatively high frequencies. This new driver circuit is simple and robust and maintains high efficiency for a wide range of input powers. In addition, the dimming control is easily realized by modulating clock frequency. Finally, this LED driver consumes no dc current and thus provides inherent protection to LED in standby mode.     

用于植物照明的LED阵列设计

基于温室植物光学作用和光形态调节原理,设计了两种用于植物照明的发光二极管(LED)阵列.通过推导阵列的辐射照度叠加公式并根据叠加公式对阵列进行仿真优化.两种阵列均采用红蓝LED相结合的方式排列,其中阵列1红光和蓝光LED的数量比是1∶1,阵列2红光和蓝光LED的数量比是4∶1.通过光学模拟软件Tracepro对照射平面...     

A switched supply tunable red-green-blue light emitting diode driver

This paper presents a new switched supply tunable red-green-blue (RGB) light emitting diode (LED) driver. The RGB LEDs act not only as light emitting devices but also as rectifying diodes in the presented driver circuit. The RGB LED color control is realized by controlling the switched supply voltage amplitude, frequency, and duty cycle. The driver efficiency is high since the only loss in the driver circuit is the switch and can be further reduced by direct alternate current supply.     

基于LED的光谱可调光源结构研究

介绍了一个由大量LED组合而成的光谱可调光源,通过不同LED的组合产生不同光谱分布,可以模拟各种光源。该光源主要由LED屏体、光谱匹配模块以及LED控制驱动模块构成。LED屏体由2 304个窄带LED组成,通过LED数据分配卡将接收到的显示数据进行分配,并驱动屏体上的LED,以PWM的方式精确控制每一个LED的电流,实现256级及以上灰度等级显示。整个系统经初步调试,已能模拟部分光谱。该光源将具有广泛的应用前景。     

High-brightness,high-power LED-based strobe illumination for double-frame micro particle image velocimetry

There is a need for more practical, cost-effective and adaptive flow measurement instruments. Unfortunately, most of the current equipment still has to employ bulky and expensive laser systems for flow illumination. In this work we explore the practicability of using high-brightness high-power light-emitting diodes (LED) as a strobe-light illuminator within a double-frame micro particle image velocimetry (microPIV) system. A compact, cost-effective, and controllable LED driver was designed and applied to study the optical and spectral behavior of green and blue family direct-color single chip LEDs, which have excitation wavelengths corresponding to the most widely used fluorescent micro particles. To achieve strobe illumination, LEDs were subjected to high current double-pulsed operating regimes (up to 35 A at 20 μs pulse duration), which are much beyond their physical damage thresholds. We have witnessed that the blue family LEDs are more suitable for the fluorescence based microPIV experiments as they exhibit more stable spectral behavior at the double-pulsed high currents compared to the green colored LEDs. Specifically, we have observed that the spectral wavelength shift of blue family LEDs due to the high current is less severe and still enough to excite particles than that of green LEDs. Also, we have studied the relation between the pulse duration (as a means of parameter controlling signal-to-noise ratio) and the motion blur effect that arises due to the prolonged pulse durations. As a result, adequate pulse durations for most widely used microPIV experimental conditions were calculated. The feasibility and robustness of the developed double-pulsed LED illumination system was validated through a series of microPIV experiments with real flows inside two different topology microchannels, where the measured velocity was in good agreement with the corresponding analytical solutions. Overall, we can conclude that the high-brightness LED devices are promising candidates to replace their laser counterparts in the microPIV systems.     

Multidie LED combined with homogenizing optics to improve frequency response and intensity for FLIM applications

Application of light‐emitting diodes (LEDs) in frequency‐domain fluorescence lifetime imaging microscopy (FLIM) has been limited by the trade‐off between modulation frequency and illumination intensity of LEDs, which affects the signal‐to‐noise ratio in fluorescence lifetime measurements. To increase modulation frequency without sacrificing output power of LEDs, we propose to use LEDs with multiple dice connected in series. The LED capacitance was reduced with series connection; therefore, the frequency response of multidie LED was significantly increased. LEDs in visible light, including blue, green, amber and red, were all applicable in FLIM. We also present a homogenizing optics design, so that multidie LEDs produced uniform illumination on the same focal spot. When the homogenizing optics was combined with multicolour emitters, it provides multiple colour selection in a compact and convenient design.     

Junction temperature measurement of light emitting diode by electroluminescence

Junction temperature (JT) is a key parameter of the performance and lifetime of light emitting diodes (LEDs). In this paper, a mobile instrument system has been developed for the non-contact measurement of JTs of LED under LabVIEW control. The electroluminescence (EL) peak shift of the LED is explored to measure the JT. Commercially available high power blue LEDs are measured. A linear relation between emission peak shift and JT is found. The accuracy of the JT is about 1 °C determined by the precision of the emission peak shift, ±0.03 nm, at 3σ standard deviation for blue LED. Using this system, on-line temperature rise curves of LED lamps are determined.     

LED在线测试中的PLF测量不确定度分析

分析了LED定位不确定度,探头光谱失配和LED快速测试上电脉冲三方面对LED在线测试中部分光通量(PLF)测量不确定度的影响,并对光强分布为叶子形的LED进行了计算与实验。结果表明,5mm的水平测试位置不确定度,5°的机械轴不确定度,0.5mm的测试距离不确定度及200ms的快速测试上电脉冲一般能满足PLF测量较高的精度要求,光度探头的光谱失配会造成较大的不确定度,必要时应给予校正。所做的工作对LED在线测试具有实际指导意义。     

A computer vision system for the inspection of light emitting diodes

This paper outlines the development of a computer vision system to enhance classification criteria for the inspection of infrared light emitting diodes (LEDs). Infrared LEDs used for fibre optics and optical switches are presently classified solely on the basis of power output. This test is performed by focusing the light beam from the LED through a circular aperture onto a solar cell. The output current from the solar cell is translated into a power output reading for the LED. The approach is limited in that it provides no information about other characteristics such as the misalignment of the beam from the mechanical centre or the intensity distribution of the beam. Improved classification criteria and testing methods based on emitted light intensity distribution can be utilised in engineering revision, setting specifications, monitoring manufacturing problems and classification for different applications.     

High speed single charge coupled device Cranz-Schardin camera

This article describes an ultrahigh speed visualization system based on a miniaturization of the Cranz-Schardin principle. It uses a set of high power light emitting diodes (LEDs) (Golden Dragon) as the light source and a highly sensitive charge coupled device (CCD) camera for reception. Each LED is fired in sequence and images the refraction index variation between two relay lenses, on a partial region of a CCD image sensor. The originality of this system consists in achieving several images on a single CCD during a frame time. The number of images is 4. The time interval between successive firings determines the speed of the imaging system. This time lies from 100 ns to 10 micros. The light pulse duration lies from 100 ns to 10 micros. The principle and the optical and electronic parts of such a system are described. As an example, some images of acoustic waves propagating in water are presented.