1,721,028 research outputs found
LED-Based Luminaire Color Shift Acceleration and Prediction
No full textColor stability is of major concern for LED-based products. Currently, much effort is done on lumen maintenance, and for color shift, no agreed method currently exists, be it from testing or from prediction side. To investigate the physics of color shift, we present experiments of each individual part failure of each individual part that are present in LED-based products. In order to develop a color shift prediction method, it is imperative to investigate the color shift contribution by each individual part. We present a new method to predict color shift on a system level, which we named the view factor approach. We compare this prediction method with experiments on luminaire level to conclude that we have taken satisfactory first steps in the field of color shift predictions for LED-based systems.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Reliability Prediction of Integrated LED Lamps with Electrolytic Capacitor-Less LED Drivers
No full textThis chapter investigates the reliability of the integrated LED lamps with electrolytic capacitor-less LED drivers. Firstly, the impact of the interaction between the degradations of the LED light source and the driver on the lumen depreciation is studied. The electronic-thermal simulation was carried out to obtain the history of temperatures of LED and driver, the driver’s output current, and the luminous flux considering the variations of temperature and current throughout the operation life. It is found that the ultimate lamp’s lifetime is significantly less than the individual lifetimes of the preselected LED and driver. It is concluded that it is necessary to apply the electronic-thermal simulations to predict the lifetime of LED lamps when driver’s lifetime is comparable to the LED’s lifetime. Secondly, this chapter focuses on predicting the catastrophic failure of an electrolytic capacitor-free LED driver during the lumen depreciation process. Electronic-thermal simulations are utilized to obtain the lamp’s dynamic history of temperature and electrical current for two distinct modes: constant current mode (CCM) and the constant optical output (CLO) mode, respectively. A fault tree method is applied to calculate the system’s MTTF, and the LED’s lifetime also is calculated. The CLO mode increases the LED’s current exponentially to maintain the constant light output. As a result, junction temperatures of LEDs, MOSFET, and diode rise significantly, leading a shorter lifetime and MTTF. Compare with the current of the MOSFET, the increased junction temperature has larger effects on the failure rate. The MOSFET contributes more to the driver’s failure rate than the diode. For the CCM mode, junction temperatures increase slightly and have a little shorter lifetime and MTTF.Electronic Components, Technology and Material
Statistical Analysis of Lumen Depreciation for LED Packages
No full textCommercial claims for LED-based products in terms of lumen maintenance are fully based on TM-21 extrapolations using LM-80 data. This chapter indicates that there may be a risk in doing this as TM-21 only relies on the behavior of the average LED degradation, instead of taking into account the degradation of all individual LEDs. Therefore, we propose a more profound statistical approach in order to make the appropriate step from TM-21 extrapolation to lumen maintenance on a product level. This is needed as some commercial claims are based on 10 years of warranty and some service bids provide periods of 20–25 years of operation. This chapter reviews the different approaches currently available to perform lumen maintenance extrapolations.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Corrosion Sensitivity of LED Packages
No full textThe penetration of solid state lighting applications is due to the promise of a low-cost reliable solution by means of application of low- and mid-power LEDs. These LED packages are manufactured by making use of new processes and materials which in principle introduces a series of known and unknown failure modes. Corrosion is a specific failure mode which limits the lifetime, and hence manufacturers realize that their package integrity needs to be improved. This chapter describes the sensitivity to corrosion of LED packages. In the first part, an introduction to chemical incompatibility is given. In the second part, different sources of corrosion are distinguished. The construction of LED packages and their vulnerability to corrosion is described in the third part. In the fourth part of this chapter, testing methods are reviewed and their effectiveness to simulate real-life conditions. A series of experimental setups is used to explore the behavior of LED packages in contaminated environments. A combined experimental–theoretical approach is used to describe the performance in certain conditions of pollution. This will be covered in the fifth part. The last part describes a list of classes of chemicals, often found in electronics and construction materials for luminaires that may affect LED performance and for this reason should be avoided for the design of SSL solutions.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
The Next Frontier: Reliability of Complex Systems
No full textTraditional lighting is focused on the prevention of hardware failures. With the trend toward controlled and connected systems, other components will start playing an equal role in the reliability of it. Here reliability need to be replaced by availability, and other modeling approaches are to be taken into account. Software reliability can only be covered by growth models, with the Goel-Okumoto as a promising candidate. System prognostics and health management is the next step to service the connected complex systems in the most effective way possible. In this chapter we highlight the next frontiers that will need to be taken in order to move the traditional lighting catastrophic failure thinking into a thinking more toward new ways how system (degraded) functions can fail or be compromised.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Reliability and Lifetime Assessment of Optical Materials in LED-Based Products
No full textLumen depreciation is one of the major failure modes in light-emitting diode (LED) systems. It originates from the degradation of the different components within the system, including the chip, the driver, and the optical materials (i.e., phosphorous layer). The kinetics of degradation in real-life applications is relatively slow, and in most cases, it takes several years to see an obvious deterioration of optical properties. A highly accelerated stress testing (HAST) setup and a methodology to extrapolate the results to real applications are therefore needed to test the reliability of LED package and lens materials. Employing HAST concept in LED industry is inevitable due to the necessity of assessing the reliability of new products in a short period of time. This chapter aims at briefly explaining the degradation mechanism of optical components in LED package and how they contribute to the lumen depreciation of the LED package. The concept of HAST and the way the reliability of LED packages can be assessed will also be explained.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Lightning Effects on LED-Based Luminaires
No full textThis chapter gives an extensive overview into the nature of the environment that luminaires and thus LEDs are subjected to during the event of a lightning stroke. Direct lightning stroke almost always results in instant damage for low-voltage connected devices, except in “extraordinary circumstances” where random components may survive. This is usually not a subject for debate and is not the subject of this monograph. Indirect consequences of lightning strokes, however, can be effectively mitigated as described. This chapter also delves into a realistic expected overvoltage levels for two typical systems, overhead lines and insulated cables, as obtained from lightning studies on a power network supplying power to LED devices and thus justifies the recommendations by several standards. In addition, it shows the importance of an often neglected device—MOV in mitigating attendant surges due to lightning to a level that can be withstood by LEDs and associated devices.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Quality and Reliability in Solid-State Lighting: Qua Vadis?
No full textIn the past 4 years we have witnessed a change in quality and reliability to make the marked introduction of solid-state lighting (SSL) successful. LED penetration levels have reached values of 10–30%, depending on the application. The number and variety of LED packages and, thus, associated LED-based products, have significantly increased in the past years. Consequently, new processes and new materials are introduced which will introduce a new series of new and unknown failure modes in SSL products. The understanding of these failure modes is better understood, and the number has grown to beyond 50. The fingerprint is changing to failures that are due to interactions between components. First exercises with system level acceleration tests are presented, but it is important to derive acceleration models for these tests. Advanced reliability prediction capabilities are needed including algorithms and tools that couple the multi-physic and multiscale behavior of the SSL failure modes. The shift toward services will force the lighting industry to develop these capabilities in order to better address lifetime and reliability. Connected lighting will bring big data from live connections that can be used to determine the degradation level of the system. Both trends, service and connected, will bring yet another huge change in mind-set in the lighting industry when in concerns reliability: detailed understanding of failure mechanisms, usage scenarios, technology, and design will come together.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and Material
Flow Modulation and Mixing Enhancement of Highly Underexpanded Jet by Vortex Excitation
No full textA highly underexpanded jet with a nozzle pressure ratio of 5.60 is excited by a vortex excitation. Modulations on flow characteristics by the vortex excitation are revealed by comparing the excited jet with the free jet through a large-eddy simulation (LES) technique. The modeling results have achieved good agreements with the available literature data in terms of time-averaged near-field variables, Mach disk dimensions, and dominant frequencies. A grid-convergence study is also performed to verify the fidelity of LES results. Ultimately, qualitative and quantitative comparisons of mean and instantaneous jet fields are conducted. It is demonstrated that the vortex excitation has enhanced the mixing of the injection nitrogen with the environment by a considerably increased mixing level and a faster mixing process in the middle jet. The vortex excitation modulates the buildup process of shocks and vortex structures, resulting in an intensified shock/shear-layer interaction and an accelerated turbulence transition process, which combine to improve mixing efficiency. The dominant instability mode is altered to a higher-order multiple helical mode from a single helical mode, and an intensified screech tone is achieved by the vortex excitation
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