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Average color coordinate shift paths of Lamp B in various stress-loaded conditions on the color map of CIE 1976.
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![Fig. 1. SUSADT profile (inset: test setup schematic) 15].](profile/Miao-Cai-5/publication/311358803/figure/fig1/AS:435263089451008@1480786215969/SUSADT-profile-inset-test-setup-schematic-15_Q320.jpg)
The color coordinate shift of light-emitting diode (LED) lamps is investigated by running three stress-loaded testing methods, namely, step-up stress accelerated degradation testing, step-down stress accelerated degradation testing, and constant stress accelerated degradation testing. A power model is proposed as the statistical model of the color...
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... average color coordinate shift paths of Lamp B with weak CHD exhibit a two-phase law (Phase I and Phase II) for all aging conditions (Fig. 5). The color coordinates first shift toward bluish light in Phase I, and then shift back toward yellowish light in Phase II. The CS kinetic of Phase I is associated with the CS process of Lamp A. The CS mechanisms of Lamp B are more sensitive to thermal stress than those of Lamp A. The result from HADT on Lamp B (Fig. 6) provides a clear ...
Citations
... High LED junction temperature degrades devices and leads to parametric failures, such as lumen depreciation and chromaticity changes, or even catastrophic failures, e.g., die delamination and broken connections resulting from thermal stress [9,10]. Moreover, considering that lighting components are frequently manufactured as assemblies containing several LEDs soldered to a common substrate and enclosed in a single housing or package, thermal interactions between individual diodes play an important role. ...
Light Emitting Diodes (LEDs) are the most commonly used light sources. Temperature strongly affects their operation. Considering that multiple devices are often placed in a single housing, thermal couplings between devices become important. This problem is illustrated here based on the example of a light source containing four LEDs in a single package. Thermal analyses are carried out based on measured transient temperature responses. The measurement results are processed employing the Network Identification by Deconvolution method. The obtained results demonstrate clearly that depending on the device mounting manner and applied cooling condition the temperature rise value induced in neighboring devices can exceed 70% of the rise in the heating diode. Consequently, thermal models of such LEDs should consider not only self-heating effects, but also thermal interactions with the other diodes.
... Changes of Y/B are estimated as 2.0%, 4.3%, and 5.6% for CSA-1, CSA-2, and CSA-3, respectively. They imply that PCE slightly decreases after aging, because of the wavelength shift of blue LED chips after 3840 h aging [28]. The higher the aging current becomes, the more decrease PCE exhibits. ...
We have experimentally analyzed multi-azimuth degradation mechanisms that govern failures of commercially-available high-power (1 Watt) phosphor-coated white (hppc-W) light-emitting diodes (LEDs) covered with peanut-shaped lenses under three current-stress aging (CSA) conditions. Comprehensive analyses focus on photometric, chromatic, electrical, thermal and packaging characteristics. At the packaging level, (a) the decrease of the phosphor-conversion efficiency; (b) the yellow-browning of the optical lens; and (c) the darkening of the silver-coated reflective layer deposited with extraneous chemical elements (e.g., C, O, Si, Mg, and Cu, respectively) contribute collectively to the integral degradation of the optical power. By contrast, Ohmic contacts, thermal properties, and angles of maximum intensity remain unchanged after 3840 h aging in three cases. Particularly at the chip level, the formation of point defects increases the number of non-radiative recombination centers, and thus decreases the optical power during aging stages. Nevertheless, in view of the change of the ideality factor, the Mg dopant activation and the annealing effect facilitate the increase of the optical power in two specific aging stages (192 h~384 h and 768 h~1536 h). This work offers a systematic guidance for the development of reliable LED-based light sources in general-lighting areas.
... Recently, C. Qian et al. proposed a method to decompose the SPD of LED lamp with the asymmetric Gaussian model and predict the lumen maintenance and color coordinates by estimating the features of the proposed statistical model [18] and also used two asymmetric double sigmoidal (Asym2sig) models, representing the blue light and phosphor converted light peaks respectively, to predict the photometric and colorimetric characteristics of a pc-WLED [19]. The color coordinate shift of LED lamps aged under accelerated ageing tests was investigated by M. Cai et al., [20] and a power model was proposed to predict the color shift process of LED products. However, as reviewed, few of the current studies on SPDs can combine the failure mechanism analysis and residual color lifetime prediction together to assess the reliability of pc-WLEDs during degradation testing. ...
With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to color quality. However, most of the current available research on the reliability of LEDs is still focused on luminous flux depreciation rather than color shift failure. The spectral power distribution (SPD), defined as the radiant power distribution emitted by a light source at a range of visible wavelength, contains the most fundamental luminescence mechanisms of a light source. SPD is used as the quantitative inference of an LED’s optical characteristics, including color coordinates that are widely used to represent the color shift process. Thus, to model the color shift failure of white LEDs during aging, this paper first extracts the features of an SPD, representing the characteristics of blue LED chips and phosphors, by multi-peak curve-fitting and modeling them with statistical functions. Then, because the shift processes of extracted features in aged LEDs are always nonlinear, a nonlinear state-space model is then developed to predict the color shift failure time within a self-adaptive particle filter framework. The results show that: (1) the failure mechanisms of LEDs can be identified by analyzing the extracted features of SPD with statistical curve-fitting and (2) the developed method can dynamically and accurately predict the color coordinates, correlated color temperatures (CCTs), and color rendering indexes (CRIs) of phosphor-converted (pc)-white LEDs, and also can estimate the residual color life.
LED luminaires are considered the primary lighting solution and have replaced other traditional luminaires in all general and focused applications as they are energy-efficient and highly reliable. The lifetime of LED luminaires is decided by the quantity of light output as well as the quality of light color. The works of the researchers and the standards they have developed are carried out only on lumen-based lifetime estimation. However, the importance of color consistency of LED luminaires is most recently realized. The work presented in this article analyses the color characteristics such as Duv,
xy
chromaticity, and spectral power distribution at different accelerated and practical operating conditions. The results and analysis help to identify the primary failure criteria and reasons for possible color variations. This work is useful for industry manufacturers to improve the performance of LED luminaires by appropriate modifications in the design and thereby maintain a long-lasting health and color consistency of LED luminaires.
Silicone is commonly used in light-emitting diode (LED) package as lens and/or encapsulation owing to its high light transmittance, large refractive index, and good thermal stability. However, the effect of silicone lens aging on the lumen decay and color shift of LED package is a considerable concern for package level reliability. This study empirically investigates the effects of silicone lens aging on lumen decay and color shift of LED package under three accelerated tests, namely, the constant stress-accelerated degradation test, step-up stress-accelerated degradation test, and step-down stress-accelerated degradation test (SDSADT). Results reveal that silicone lens aging substantially contributed to lumen decay and color shift of LEDs and considerably influenced the degradation kinetics of LED package. The color coordinates of LED package covered with aged silicone specimen in three testing methods exhibit a steady yellowing shift law at the same 45-degree direction. Silicone lens aging primarily reduces its transmittance to blue light as accumulated thermal oxidation and hydrolysis reaction, and its effect on the blue peak intensity of LED is independent of the stress-loaded order of step stress-accelerated degradation testing (SSADT). In addition, the effect law of silicone lens aging on LED lumen and color shift could be presented with the exponential and power function models, respectively. Lumen decay and color shift are mostly independent of the historical stress and loaded order in SSADT. The SDSADT testing manner more effectively distinguishes the color shift effect of thermal stress level compared with other accelerated tests. These findings are assumed to benefit the design and reliability assessment of LED products.
LED luminaires are common lighting source used in general lighting application for it is energy efficient and long lasting. However, reliability of LED-Luminaire is not well established and no standard method for estimating the performance of LED-luminaire is developed. The paper presents an investigation to understand the performance of LED-luminaire at accelerated degradation test (ADT) condition and analyzes the reliability of LED-luminaire. LED luminaire has two subsystems, LED light engine and the LED constant current driver which are subjected to ADT and the light engine factors - lumen output and Duv changes are analyzed. Similarly, the driver output stage electrolytic capacitor- capacitance and ESR are estimated. The study of continuous operation in time and study when subjected to switching cycles to quantify reliability in terms of operating cycles is performed. All four key parameters - lumen maintenance, Duv, Capacitance and ESR are estimated upto their specified threshold and reliability is analyzed. The LED light engine lumen output is found to degrade very quickly compared to other factors. LED-luminaire failure at ADT is mainly due to lumen depreciation followed by colour-shift and, after significant intervals of time and cycles, the driver capacitor ESR follows as reason for failure of the LED-luminaire. SEM-EDS analysis is performed on the LED package and results show that LED silver (Ag) mirror tarnish is the main reason for significant reduction in light output.
The paper is a literary survey on publications from 2016 and 2017 about novelties in development of LEDs and illuminants of them. The results represent new functions, management methods and applications. The functions are improved in three directions: LEDs in visible spectrum, LEDs in UV part of optical spectrum and organic LED (OLED). The management includes the following: color control, color change, reducing the light flicker to low risk levels, illumination with power LEDs, management of Pulse Width Modulation, enhancement of supply efficiency, loss management, monitoring, analysis and estimation of power demand curve. At the end are listed different LED lighting applications. This creates a base for discussion about the future work in Bulgaria: qualitative and quantitative research of LED development politics and waste management.
