DESIGN AND RELIABILITY ASSESSMENT OF HIGH POWER LED AND LED-BASED SOLID STATE LIGHTING

Lumen depreciation and color quality change of high power LED-based solid state light (SSL) are caused by the combination of various degradation mechanisms. The analytical/experimental models on the system as well as component-level are proposed to analyze the complex reliability issues of the LED-based solid SSL. On the system-level front, a systematic approach to define optimum design domains of LED-based SSL for a given light output requirement is developed first by taking cost, energy consumption and reliability into consideration. Three required data sets (lumen/LED, luminaire efficacy, and L70 lifetime) to define design domains are expressed as contour maps in terms of two most critical operating parameters: the forward current and the junction temperature (If and Tj). Then, the available domain of design solutions is defined as a common area that satisfies all the requirements of a luminaire. Secondly, a physic of failure (PoF) based hierarchical model is proposed to estimate the lifetime of the LED-based SSL. The model is implemented successfully for an LED-based SSL cooled by a synthetic jet, where the lifetime of a prototypical luminaire is predicted from LED lifetime data using the degradation analyses of the synthetic jet and the power electronics. On the component-level front, a mathematical model and an experimental procedure are developed to analyze the degradation mechanisms of high power LEDs. In the approach, the change in the spectral power distribution (SPD) caused by the LED degradation is decomposed into the contributions of individual degradation mechanisms so that the effect of each degradation mechanism on the final LED degradation is quantified. It is accomplished by precise deconvolution of the SPD into the leaked blue light and the phosphor converted light. The model is implemented using the SPDs of a warm white LED with conformally-coated phosphor, obtained before and after 9,000 hours of operation. The analysis quantifies the effect of each degradation mechanism on the final values of lumen, CCT and CRI

Synthesis, properties and uses of ZnO nanorods: a mini review

Zinc oxide (ZnO) nanorods have been extensively investigated, owing to their extraordinary applications in numerous felds, spatially microchip technology, solar cells, sensors, photodetectors, photocatalysts and many others. Recently, using ZnO nanorods, as photocatalysts, are receiving increasing attention in environmental defense applications. This mini review sum�marizes some remarkable applications for ZnO nanorods. First, the various chemical and physical procedures that were used to produce ZnO nanorods are identifed through symmetric matrices and heterogeneous structures, then the authors explain how to use these methods to produce ZnO nanorods. This mini review, also, discusses the applications of ZnO nanorods in many felds, especially in feld release, emission properties, and electron transference. Last but not least, the appropriate conclusions for future research using ZnO nanorods have been successfully explained.

Identifying and evaluating aging signatures in light emitting diode lighting systems

Dans ce travail, les dégradations des diodes électroluminescentes (DEL) ont été étudiées en identifiant et en évaluant leurs signatures électriques et photométriques en vieillissement accéléré sous stress thermique et électrique. Un prototype de banc de test expérimental a été développé et construit spécifiquement pour cette étude ce qui nous a permis de tester 128 échantillons en appliquant différentes conditions de stress thermiques et électriques. Quatre types différents de DEL ont été étudié avec des caractéristiques techniques similaires (température de couleur, courant nominal, mono-puce,...) mais avec des technologies différentes couvrant les principaux acteurs du marché (Cree, Osram, Philips et Seoul Semiconductor). Les échantillons ont d'abord été caractérisés à leur état initial, puis soumis à des conditions de stress électrique (à 350mA ou 1050mA) et thermique (fixé à 50°C). Les mécanismes de défaillance ont été analysés en étudiant l'évolution des signatures électriques et photométriques. Ces caractérisations ont permis d'évaluer et de déterminer l'origine des dégradations à différents niveaux : puce semi-conductrice, interconnexions, phosphore ou encapsulation du dispositif. Les caractérisations électriques nous ont permis d'identifier les mécanismes de dégradation de la puce semi-conductrice et de déterminer la nature des dégradations au niveau du contact ohmique du dispositif (sous fort courant injecté). Les caractérisations photométriques complètent cette étude en évaluant les dégradations associées à l'optique (encapsulation et packaging).In this work, the degradation of light emitting diodes (LEDs) is studied by identifying and evaluating their aging signature during the stress time. The custom-made experimental test bench is built for realization of the test measurement. Through this experimental test bench, it allows to test a large amount of LED samples and enable to select different temperature condition and different current stress level. There are four different types of LED with similar characteristic in term of their color temperature, IF, VF, power (1W) and as monochip, but different technology coming from Cree, Osram, Philips and Seoul Semiconductor. The devices are firstly characterized their electrical and photometrical characteristic at their initial state, then they are submitted to different current stress condition at low current stress (350mA) and high current stress (1000mA) while the thermal stress is fixed at one temperature (50°C). The study of these devices failure mechanism is archived by using the primary method based on the electrical and photometrical characterization of the devices that allows to evaluate their degradation at different locations of the device components such as semiconductor chip, interconnection and device's package. The electrical characteristic of the device's I-V curve: at low injected current level and reverse bias allow us to identify the degradation characteristic of device's semiconductor chip, at high injected current level allows us to determine the degradation of device's ohmic contact and photometric characteristic allows us to evaluate the degradation of device's package system

Optoelectronics – Devices and Applications

Optoelectronics - Devices and Applications is the second part of an edited anthology on the multifaced areas of optoelectronics by a selected group of authors including promising novices to experts in the field. Photonics and optoelectronics are making an impact multiple times as the semiconductor revolution made on the quality of our life. In telecommunication, entertainment devices, computational techniques, clean energy harvesting, medical instrumentation, materials and device characterization and scores of other areas of R&D the science of optics and electronics get coupled by fine technology advances to make incredibly large strides. The technology of light has advanced to a stage where disciplines sans boundaries are finding it indispensable. New design concepts are fast emerging and being tested and applications developed in an unimaginable pace and speed. The wide spectrum of topics related to optoelectronics and photonics presented here is sure to make this collection of essays extremely useful to students and other stake holders in the field such as researchers and device designers

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Effects of silicone coating degradation on GaN MQW LEDs performances using physical and chemical analyses

International audienceThis work presents a physics of failure (POF) methodology coupling failure signatures with physico-chemical analyses. The aim is to work out electro-optical failure signatures located in packaged InGaN/GaN Multiple Quantum Wells Light Emitting Diodes (MQW LEDs). Electrical and optical characteristics performed after accelerated ageing tests (30 mA/85 °C/1500 h), confirm a 65% drop of optical power and an increase of one decade of leakage current spreading at the silicone oil/chip interfaces. Through measurements of silicone coating fluorescence emission spectra, we demonstrate that the polymer enlarges the LED emission spectrum and shifts central wavelength. This shift is related to silicone oil spectral instability and the central wavelength of packaged LED appears to be temperature insensitive. In this paper, we discriminate the degradation of bulk silicone oil responsible for optical losses from the polymer/chip interface inducing larger leakage current

Recent Progress in Optical Fiber Research

This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas