大功率LED整个寿命中的颜色漂移

为了研究大功率白光、蓝光LED在整个寿命中的颜色漂移,选用一系列的大功率白光、蓝光发光二极管分别进行了不同电流的恒流点亮。在点亮不同时间阶段测量了LED的发射光谱、色坐标和色温,研究了在不同电流点亮时的光通量、色坐标和色温的变化,分析了电流、时间等因素对颜色漂移的影响。结果表明,在不同电流点亮及同一电流点亮的不同时间阶段,LED的颜色不同。说明大功率LED的颜色漂移不仅是由荧光粉老化所引起,更主要的因素是材料本身的变化。文章对此进行了初步的分析,为白光LED的应用及进一步研究白光LED颜色漂移提供了参考。     

认识大功率LED

大功率LED是指拥有大额定工作电流的发光二极管。普通LED的功率一般为0．05W,工作电流为20mA,而大功率LED可以达到1W、2W,甚至数十瓦,工作电流可以是几十毫安到几百毫安不等。由于目前大功率LED受到光通量、转换效率和成本等方面的制约,决定了大功率白光LED短期内的应用主要是一些特殊领域的照明,中长期目标才是通用照明。     

低色温高显色性白光LED的研究

文章论述了低色温高显色性白光LED的制备方法及其发展现状与趋势,重点分析了低色温高显色性白光LED的光色电参数．并指出了低色温高显色性白光LED制备技术的难点。同时制备了瓦级大功率白光LED,其显色性高达93,经过1,000小时老化后,色温出现漂移,显色指数仍高于83。     

峰值波长和浓度对转光膜与白光LED发光性能的影响

本文以高折射率有机硅胶和无机Y3Al5O12:Ce3+发光材料为原料,采用加热固化的方法制备出有机/无机转光膜,系统的研究了发光材料的峰值波长和浓度对于转光膜和制备的白光LED光色性能的研究,并进行了机理分析。研究结果表明：不同峰值波长变量中,545nm对应白光LED最大的光通量,是由于其光谱与人眼明视觉曲线具有最大的重叠面积有关;不同浓度变量中,由于存在发光材料的吸收饱和现象,在9%浓度时白光LED最大的光通量,色温则与浓度变化呈现单向递减趋势,色坐标和光色均匀度则随着浓度的提高而提高,综合多种指标获得本研究中最佳工艺参数为峰值波长为545nm,浓度为9%,对应白光LED器件光通量为131.5lm,色温4551K,色坐标（0.3479,0.3758）,光色位置处于黑体辐射曲线的白光区,说明了转光膜在白光LED领域应用的可行性。     

低色温高显色性大功率白光LED的制备及其发光特性研究

用GaN基大功率蓝光LED芯片作为激发光源，分别用荧光粉转换法和红光LED补偿法制备了不同相关色温及显色指数的白光LED。对器件的发光特性研究表明，采用监光LED芯片激发单一黄色荧光粉，虽可以获得光通量和发光效率较高的白光LED，但其色温较高，显色性较差；在黄色荧光粉中添加红色荧光粉，由于光谱中红色成分的增加，可降低器件的色温，并提高器件的显色性，但由于目前红色荧光粉的转换效率较低，致使器件的整体发光效率不高；采用蓝光LED芯片激发黄色荧光粉，同时用红光LED进行补偿，通过调整蓝光和红光LED芯片的工作电流以及荧光粉的用量，可获得低色温和高显色性白光LED，而且整体发光效率较高。     

高亮度高纯度白光LED封装技术研究

通过对高功率InGaN(蓝)LED倒装芯片结构+YAG荧光粉构成白光LED的分析,可以得出这种结构能提高发光效率和散热效果的结论。通过对白光LED的构成和电流/温度/光通量的分析,可知在蓝宝石衬底和环氧树脂的界面间涂敷一层硅橡胶能改善光的折射率。改进光学器件的封装技术,可以大幅度提高大功率LED的出光率(光通量)。     

荧光粉发光层对白光LED平面光源发光特性的影响

以COB形式封装的白光LED平面光源为研究对象,系统研究了平面封装结构中荧光层对白光LED平面光源发光特性的影响.采用丝网印刷法制备了不同浓度与印刷层数的荧光层,并采用平面封装的LED蓝光光源作为激发光源,以类比法研究分析了不同发光层膜厚对白光平面光源平均照度、色坐标和光通量等参数的影响,系统地阐述了发光层对平面光源发光性能的决定因素及工艺优化条件.结果表明,当荧光粉浆料浓度为46％～53.6％,厚度为20～38 μm时,结合平面蓝光LED激发可以获得照度大、颜色纯正的白光LED光源,且白光LED平面光源具有较高的光通量值,表现出优良的光学特性.     

三芯片集成高显色指数白光LED的研究

运用基于蒙特卡罗的光线追迹方法,对采用"光转换"兼"多色混合"技术的白光LED的显色指数、相关色温、光通量、光辐射功率、荧光粉颗粒密度和色坐标进行了仿真计算和优化选择。通过改变红、绿、蓝三种LED芯片的组合方式和红、绿、黄三种荧光粉的混合方式及各色荧光粉的密度,在保证有合理的光通量输出的条件下,得到了不同色温区的高显色指数白光LED。从显色指数角度看,冷白、正白和暖白光应分别选择BBB芯片+绿、红色荧光粉、BBB芯片+黄、红色荧光粉和RBB芯片+黄色荧光粉组合。实验上测试了采用这几种组合方式的白光LED光谱、显色指数、色温、光通量和色坐标,实验数据与仿真结果基本吻合。     

直下式LED背光TV色域的研究

分析了影响直下式LED背光TV色域的各种因素,研究了光学材料与液晶面板对白光色度坐标的影响,结果表明光学材料、液晶面板对白光色坐标的平均偏差值分别为(-0.0285,0.0270)、(0.0139,0.0015);研究了光学材料、LED光源以及液晶面板对TV色域的影响,结果表明:(1)不同厂家光学材料色域差距仅为0.2%;(2)不同液晶面板贴合相同的LED背光,色域相差22.8%;(3)从白光两波段LED到三波段LED再到RGB LED的背光,色域依次从75.3%、84.2%、104.5%。因此,要实现特定的色彩,需综合考虑每个部分对白光色度坐标的影响;另外,要获得高的色域范围,需选取与液晶面板相对应的LED光源。     

一体化封装LED结温测量与发光特性研究

基于一体化封装基板,制备了大功率白光LED。以低热阻的一体化封装基板为基础,设计了结温测量系统。利用光谱仪测得不同结温下LED的光电参数,并对其机理进行了分析。在工作电流为0.34A,所研究温度范围为10.8～114.9℃。实验结果表明,一体化封装的LED结温与正向电压、光通量、光效和色温有着良好的线性关系;结温的变化对主波长及色坐标影响甚微;结温的上升导致蓝光段强度下降且光谱发生红移,黄光段强度上升且光谱发生宽化,峰值波长由450nm转为550nm。     

荧光粉浓度和电流强度对白光LED特性的影响

讨论了荧光粉浓度及驱动电流强度对白光LED特性的影响。采用软件模拟实验和实际封装测试相结合的研究方法进行分析研究。对荧光粉浓度变化对白光LED光通量和相关色温(CCT)的影响进行了三维光线追迹模拟,并且进行了实际的封装验证。另外对白光LED的节温和显色性也做了深入细致的研究。研究结果表明:CCT随着荧光粉浓度的增大而减小,光通量则先上升后下降。同时由荧光粉浓度和驱动电流强度变化所引起的节温升高会降低荧光粉的转换效率。对显色性而言,采用高浓度荧光粉封装的白光LED有相对低的显色指数;并且显色指数随着驱动电流强度的增加而升高,最终趋于稳定。     

荧光粉配比对大功率白光LED发光特性的影响

利用黄色、红色和黄绿色3种荧光粉混合的方法制备了一系列大功率平面发光LED光源,深入研究了黄色、红色和黄绿色3种荧光粉分别对大功率白光LED光源的发光效率、显色指数以及色温的影响规律。研究结果表明,随着黄色荧光粉含量的增加,其发光效率明显提高,最高可达140 lm/W,而显色指数和色温略有下降。随着红色荧光粉含量的增加,其显色指数明显提高,最高可达85,而发光效率和色温明显降低。随着黄绿色荧光粉含量的增加,其发光效率、显色指数以及色温均不同程度地略有下降,但是其对大功率白光LED的色容差起到很好的调节作用。     

A design and qualification of LED flip Chip-on-Board module with tunable color temperatures

with the increasing requirements on guaranteeing the color uniformity and improving the luminous efficacy and manufacturing efficiency, a wafer level chip scale packaging (WLCSP) technology has been developed by thermally impressing a thin multiple phosphor film on a LED wafer, then being segmented into individual LED chips. In this paper, a high power white LED Chip-on-Board (COB) module with high color rendering index (CRI, Ra > 93) and tunable correlated color temperatures (CCTs) is prepared by the flip chip technology. In this COB module, the tunable color temperatures are achieved by using two types of white LED CSPs with different target CCTs of 3000 K and 5000 K. The thermal and photochromatic properties and the photochromatic stability of the COB module are studied through both experiments and simulations. The results show that: 1) The measured spectral power distribution (SPD) intensity of the prepared COB module is smaller than the arithmetic sum of SPD intensities of its each series connected CSPs, which may be attribute to the light absorption happened among CSPs; 2) The junction temperature and driven current have the different effects on the photochromatic properties of COB module (i.e. luminous flux, CCT and CRI); 3) The nonlinearity of luminous flux as a function of driven current and junction temperature should be considered in its modeling.     

COB封装全光谱LED光源及其光电特性

为了提高光源的显色指数,设计、制作一种COB封装的全光谱LED光源,通过在设计中增加峰值波长415nm的紫光LED芯片和发光峰值波长497nm、655nm的荧光粉,弥补了普通LED光源在紫光、蓝绿光和红光等光谱区间的能量分布不足。实验结果表明,发光效率达到103.34lm/W,全光谱LED光源显色指数高达99.38,接近日光100的显色指数,能够满足高质量照明领域对光源显色性的要求。     

Correlated Color Temperature Tunable Multi-chip Light Emitting Diodes Light Source Design

One of the methods to derive white light from light emitting diodes（LEDs） is the multi-chip white LED technology, which mixes the light from red, green and blue LEDs. Introduced is an optimal algorithm for the spectrum design of the multi-chip white LEDs in this paper. It optimizes the selection of single color LEDs and drive current controlling, so that the multi-chip white LED achieves the target correlated color temperature （CCT）, as well as high luminous efficacy and good color rendering. A CCT tunable LED light source with four high-power LEDs is realized based on the above optimal design. Test results show that it maintains satisfactory color rendering and stable luminous efficacy across the whole CCT tuning range. Finally, discussed are the design improvement and the prospect of the future applications of the CCT tunable LED light source.     

Color rendering and luminous efficacy of trichromatic and tetrachromatic LED-based white LEDs

White light-emitting diode (LED) spectra for general lighting should be designed for high luminous efficacy as well as good color rendering, which are generally in a trade-off relationship. White LEDs have uncountable metameres, they have different luminous efficacy and color rendering. Appropriate designed trichromatic and tetrachromatic LED-based white LEDs are presented that have acceptable color rendering as well as good luminous efficacy. Triachromatic white LEDs, with a wavelength combination of 460, 540, and 615 nm, offer high general color rendering index exceeding 89, and luminous efficacy 336 lm/W. The general color rendering index of tetrachromatic LED-based white LEDs combined from 460, 525, 590, and 640 nm is 95, the luminous efficacy is 306 lm/W. Further analysis shows the changing trends of the luminous efficacy, color rendering and the chromaticity coordinate of the optimized trichromatic and tetrachromatic white LEDs depending on the wavelength shift of the primary LEDs. For the optimized trichromatic white LEDs, both the luminous efficacy and color rendering change more with the wavelength shifts of the primary red LEDs than with the wavelength shifts of the blue and green LEDs. For the optimized tetrachromatic white LEDs, the changes of the luminous efficacy caused by the wavelength shifts of one red LED are smaller than the changes of trichromatic white LEDs. And the wavelength shifts of the red primary LED that have shorter wavelength affect the color rendering more than the other primary LEDs. The wavelength shifts of the blue primary LED change the chromaticity coordinate of the white LEDs more. The small changes of the chromaticity coordinate of the white LED do not mean small changes of the k and R_a.     

COB封装对LED光学性能影响的研究

针对LED高光效、低功耗的要求,文章在分析LED光学性能的基础上,采用了COB(ChipOn Board)即板上芯片封装技术。研究了不同封装工艺和材料,分析比较其对LED光通量、光效和色温的影响。研究首先介绍COB封装的结构、优点及其实用性,然后分析影响LED光学性能的因素,最后进行测试。在实验过程中,发现COB封装结构除了具有保护芯片的功能外,还可以提高出光效率,并实现特定的光学分布。实验结果表明:文章提出的封装工艺对于提高光通量和光效、调节色温有良好的效果。     

Nitride-based cascade near white light-emitting diodes

An InGaN-GaN blue light-emitting diode (LED) structure and an InGaN-GaN green LED structure were grown sequentially onto the same sapphire substrate so as to achieve a nitride-based near white LED. In order to avoid thyristor effect, we choose a large 2.1×2.1 mm² LED chip size, which was six times larger than that of the normal LED. It was found that we could observe a near white light emission with Commission International de l'Eclairage color coordinates x=0.2 and y=0.3, when the injection current was lower than 200 mA. It was also found that the output power, luminous efficiency and color temperature of such a cascade near white LED were 4.2 mW, 81 l m/W, and 9000 K, respectively     

Luminous efficacy and color rendering index of high power white LEDs packaged by using red phosphor

We packaged a series of high power white LEDs by covering the blue LED chips with yellow phosphor, red phosphor and the two phosphors mixed by appropriate mass ratio,respectively,and discussed the excitation and emission spectrum of yellow phosphor and red phosphor and the characteristics of the LEDs.We found that the luminous efficacy of the white LEDs covered with the two phosphors mixed by appropriate mass ratio was lower than that of the white LEDs covered with yellow phosphor,but the color rendering index was improved observably.