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.     

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。     

两基色白光LED的配色研究

从色度学原理出发,简述了两基色白光LED的配色原理,确定了可合成白光的两基色的选取范围和两基色的配比范围,计算分析了两基色白光LED的光视效能和一般显色指数。两基色白光LED具有较高的光视效能,但其显色性却较差,主波长为450 nm左右的蓝光LED与主波长572 nm左右的黄绿光混合得到的白光的光视效能值最大,约为400 lm/w,已接近等能纯白点的理论极值,但一般显色指数只有—0.5。主波长为480 nm左右的LED与主波长为580 nm左右的LED混合得到的白光的一般显色指数值最大,仅为16.2。     

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.     

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。     

高亮度白光LED色温动态可调及显色指数的研究

采用基于高亮度白光LED的色温可调混色方法,通过实验与理论计算研究了不同色温白光LED混色后色温Tc及显色指数Ra的变化。采用低色温（2 800～3 000K、3 000～3 400K）和高色温（7 000～8 000K）三种白光LED样品进行串联和并联混色,通过控制正向工作电流研究混色后白光的调光效果及显色指数变化。实验与计算表明：混色后白光色温可以实现在3 000～7 000K可调;选取Ra〉66的低色温白光LED与Ra〉87的高色温白光LED进行混色,可以在色温可调范围内得到Ra〉75的较好显色指数的白光。     

多芯片集成大功率白光LED照明光源

通过对自行设计的集成功率型1W白光LED进行测试，发现当持续点亮900h时，其光通量衰减只有12％，比传统支架型封装的白光LED明显慢，而色温飘移也不明显。1W白光LED的色温可以覆盖2700～13000K，并且显色指数均可做到80以上，完全能够满足普通照明对光性能指标的要求。通过对多颗小功率芯片(60mW)进行不同的串并联组合，可以实现不同的额定电压与电流，可以更好地匹配驱动器的设计，提高整体发光效能，降低成本，并满足不同场合的需求。最后给出了3个典型LED驱动设计实例。     

白光LED封装用蛾眼化荧光玻璃制备及光学性能

针对荧光玻璃封装白光LED存在的全反射损耗问题,制备了一种蛾眼化荧光玻璃用于提高白光LED光学性能。采用光刻和刻蚀工艺在蓝宝石基片的单面上制作出蛾眼阵列结构,再利用丝网印刷和低温烧结工艺在蓝宝石的另外一面制备YAG∶Ce^3+荧光玻璃层,最后将制备的蛾眼化荧光玻璃用于白光LED封装。通过控制荧光层厚度可以有效调节白光LED发光性能,当荧光层厚度为40μm时,白光LED光效为77.8 lm/W,色温为6024 K,显色指数为69.5。与平面荧光玻璃封装结构相比,在100 mA电流下蛾眼化荧光玻璃封装结构的光效提高了24.9%。结果表明,蛾眼化荧光玻璃提高了白光LED光效,有利于促进荧光玻璃封装白光LED的实际应用。     

双通道PWM的冷暖白光LED混色模型研究

LED光色度的动态调节是实现智能照明的基础, 采用冷暖白光LED和双通道脉冲宽度调制(PWM)法,基于1931CIE标准建立混合光源模型,推导出混合光源色坐标、相关色温 、最大亮度、显色指数与双通道调制脉冲 占空比比值的关系式。采用暖白光(色温3282 K)和冷白光(色温12930K)两种白光LED进行 混色实验, 通过微控制器输出PWM信号控制LED驱动电源,改变冷色光和暖色光的比重,得到的混合 光源色坐 标、最大亮度、相关色温及显色指数值与理论计算值吻合很好,证明了理论模型的正确性。 理论和实验结 果还表明,混合光源在双通道调制脉冲占空比比值为1的附近可得到低色温、高显色性和大 光通量的混合白光。     

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.     

白光LED荧光粉远场涂覆光学性质

研究了白光LED远场隔离封装中隔离距离对发光效率及相关色温(CCT)的影响。实验结果表明,低电流输入条件下,白光LED的发光效率随芯片表面到荧光粉层距离变化是非线性的,当芯片表面到荧光粉层距离为0.88mm时具有最佳发光效率74lm/W,白光LED相关色温随着距离的增加呈线性下降。这为白光LED的一次光学设计提供了实验依据。     

实现白光LED阵列色温分布均匀化技术研究

本文通过优化白光LED阵列的结构,实现在目标面上产生均匀的色温分布。通过收集系统中每颗LED的色温坐标矩阵与照度矩阵,根据色温叠加公式,计算LED阵列在目标面上叠加后的色温分布,构建目标面上色温均匀度评价函数,评价函数反应目标面上色温分布的均匀性。通过优化阵列中LED的位置,使得评价函数的值最小,即目标面上色温均匀度最高。运用这种方法我们优化设计了两个实例:(1)相同规格的9颗白光LED方形阵列;(2)不同规格16颗圆形白光LED阵列,优化后色温均匀度均达到了95%以上。利用这种方法同样可以在目标面上同时实现均匀的色温分布与照度分布,设计9颗相同规格的白光LED以3×3方形阵列方式排布,优化后色温均匀度从78%提升到88.7%,照度的均匀度从42%提升到87.6%。分析实际加工制造过程产生的误差对色温均匀度的影响,随着制造误差的增大优化后色温均匀度下降,但均优于优化前色温分布均匀性。     

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。     

一种色温可调LED的封装与性能研究

LED以其优良的性能结合智能控制系统,被越来越多地应用于室内外照明场合,但同时也对其色温、显色指数等色度指标提出了新的要求.为了应对这种挑战,设计了一种新型的色温可调LED,利用大功率LED芯片结合金属基板封装出了色温可调的暖白光高显色指数LED样品,对其发光光谱、色温和显色指数随电流的变化进行了测试,发现LED的光谱...     

高亮度InGaN基白光LED特性研究

利用自行研制的InGaN GaNSQW蓝光LED芯片和YAG :Ge3 荧光粉制作了高亮度白光LED(Φ3) ,并对其发光强度、色度坐标、I V、色温及显色性等特性进行了研究 .实验结果表明 :室温下 ,正向电流为 2 0mA时 ,白光LED的轴向发光强度为 1 1～ 2 3cd ,正向电压小于 3 5V ,色度坐标为 (0 2 8,0 34) ,显色指数约为 70 .     

多基色白光LED的配色研究

利用基色光混色的方法对三基色和四基色白光LED进行了配色研究。固定相关色温为(5 500±20)K的条件下,在可见光范围内将不同峰值波长、半宽的基色光进行混色,得到显色指数和光视效能与峰值波长和半宽的关系。其中,三、四基色白光LED的显色指数最高分别达到89和96.7,对应的光视效能分别为353lm/W和340lm/W。同时,计算结果表明,增加基色光的数目后,提高了白光LED的显色性及显色稳定性。     

Improvement of emission efficiency and color rendering of high-power LED by controlling size of phosphor particles and utilization of different phosphors

White light can be produced by a combination of red, green and blue emitting diode chips or by the combination of a single diode chip with phosphors. Presently, more single chip white light-emitting diodes (LEDs) than multi-chip one are used because of their low cost, easily controlled circuitry, ease of maintenance and favorable luminescence efficiency. Since phosphors must be used as light converting materials in a single diode chip to obtain the desired emission, this study considers the problems encountered in using phosphors in LEDs. The proper application of phosphors in the package of LED can improve its efficiency, color rendering and thermal stability of luminescence. For example, a uniform size distribution of phosphors with red, green and blue emission helps to improve luminescence efficiency by preventing cascade excitation; the change in color with temperature can be overcome by counter-balancing red-shifting and blue-shifting phosphors; larger particles help to ensure the high efficiency of high-power LEDs, and costs can be reduced by using small particles size in low-power LED packaging because allows less phosphor to be used to obtain a particular efficiency.     

A General Photo-Electro-Thermal Theory for Light Emitting Diode (LED) Systems

The photometric, electrical, and thermal features of LED systems are highly dependent on one another. By considering all these factors together, it is possible to optimize the design of LED systems. This paper presents a general theory that links the photometric, electrical, and thermal behaviors of an LED system together. The theory shows that the thermal design is an indispensable part of the electrical circuit design and will strongly influence the peak luminous output of LED systems. It can be used to explain why the optimal operating power, at which maximum luminous flux is generated, may not occur at the rated power of the LEDs. This theory can be used to determine the optimal operating point for an LED system so that the maximum luminous flux can be achieved for a given thermal design. The general theory has been verified favorably by experiments using high-brightness LEDs.      

Status and prospects for phosphor-based white LED packaging

The status and prospects for high-power, phosphor-based white light-emitting diode (LED) pack-aging have been presented. A system view for packaging design is proposed to address packaging issues. Four aspects of packaging are reviewed: optical control, thermal management, reliability and cost. Phosphor materials play the most important role in light extraction and color control. The conformal coating method improves the spatial color distribution (SCD) of LEDs. High refractive index (RI) encapsulants with high transmittance and modified surface morphology can enhance light extraction. Multi-phosphor-based packaging can realize the control of correlated color temperature (CCT) with high color rendering index (CRI). Effective thermal management can dissipate heat rapidly and reduce thermal stress caused by the mismatch of the coefficient of thermal expansion (CTE). Chip-on-board (COB) technology with a multi-layer ceramic substrate is the most promising method for high-power LED packaging. Low junction temperature will improve the reliability and provide longer life. Advanced processes, precise fabrication and careful operation are essential for high reliability LEDs. Cost is one of the biggest obstacles for the penetration of white LEDs into the market for general illumination products. Mass production in terms of CoB, system in packaging (SIP), 3D packaging and wafer level packaging (WLP) can reduce the cost significantly, especially when chip cost is lowered by using a large wafer size.     

固定相关色温下三基色合成白光LED的光谱优化

通常获得白光LED的高光视效能（K）往往是以降低其显色指数（Ra）为代价的,本文在固定相关色温（CCT）为3 000±10 K下,通过调配三基色白光LED光谱参数来寻求K和Ra的最佳平衡。模拟结果表明：当三基色白光LED的3个峰值波长分别为467、550和618 nm,半高宽（FWHM）分别为30、71和23 nm以及...