A practical degradation based method to predict long-term moisture incursion and colour change in high power LEDs

The effect of relative humidity on LEDs and how the moisture incursion is associated to the color shift is studied. This paper proposes a different approach to describe the lumen degradation of LEDs due to the long-term effects of humidity. Using the lumen degradation data of different types of LEDs under varying conditions of relative humidity, a humidity based degradation model (HBDM) is developed. A practical estimation method from the degradation behaviour is proposed to quantitatively gauge the effect of moisture incursion by means of a humidity index. This index demonstrates a high correlation with the color shift indicated by the LED's yellow to blue output intensity ratio. Physical analyses of the LEDs provide a qualitative validation of the model, which provides good accuracy with longer periods of moisture exposure. The results demonstrate that the HBDM is an effective indicator to predict the extent of the long-term impact of humidity and associated relative color shift

Effects of Humidity on the Electro-Optical-Thermal Characteristics of High-Power LEDs

LEDs are subjected to environments with high moisture in many applications. In this paper, the experiments reveal photometric and colorimetric degradation at high humidity. Corresponding spectral power analysis and parameter extraction indicate that the flip-chip bonded LED samples show accelerated chip failure compared to the conventionally bonded samples. The chip-related failure induces greater heat accumulation, which correlates with the increase in heating power observed in the package. However, the temperature rise and thermal resistance for the flip-chip bonded LEDs do not increase substantially as compared to the conventionally bonded LEDs. This is because the junction temperature can be reduced with a flip-chip die-bonding configuration where the heat generated in the LED chip is dissipated effectively onto the AlN substrate, thereby reducing the increase in temperature rise and thermal resistance. The experimental results are supported by evaluation of the derivative structure functions. In addition, as the thermal resistance of the LED package varies with different humidity levels, there is a need to specify the conditions of humidity in data sheets as LED manufacturers routinely specify a universal thermal resistance value under a fixed operating condition

Prognostics and health management of light emitting diodes

Prognostics is an engineering process of diagnosing, predicting the remaining useful life and estimating the reliability of systems and products. Prognostics and Health Management (PHM) has emerged in the last decade as one of the most efficient approaches in failure prevention, reliability estimation and remaining useful life predictions of various engineering systems and products. Light Emitting Diodes (LEDs) are optoelectronic micro-devices that are now replacing traditional incandescent and fluorescent lighting, as they have many advantages including higher reliability, greater energy efficiency, long life time and faster switching speed. Even though LEDs have high reliability and long life time, manufacturers and lighting systems designers still need to assess the reliability of LED lighting systems and the failures in the LED. This research provides both experimental and theoretical results that demonstrate the use of prognostics and health monitoring techniques for high power LEDs subjected to harsh operating conditions. Data driven, model driven and fusion prognostics approaches are developed to monitor and identify LED failures, based on the requirement for the light output power. The approaches adopted in this work are validated and can be used to assess the life of an LED lighting system after their deployment based on the power of the light output emitted. The data driven techniques are only based on monitoring selected operational and performance indicators using sensors whereas the model driven technique is based on sensor data as well as on a developed empirical model. Fusion approach is also developed using the data driven and the model driven approaches to the LED. Real-time implementation of developed approaches are also investigated and discussed

Green Production: LED Application

Advances in light emitting diode (LED) technology have made LEDs a viable option for energy efficient illumination. Light fixtures utilizing LEDs were designed and prototyped to replace incandescent factory task lights and fluorescent stairway lights at a Central Industrial Supply factory in Wuxi, China. Emphasis was placed on LED selection, circuit design, and heat dissipation. Energy savings of 85.2% for the factory task lights and 38.9% for the stairway lights were achieved with a combined payback period of 2.5 years

Solid State Lighting: A Summarization of Advancements

Solid State Lighting is a rapidly growing new technology in the field of lighting. By utilizing the concepts of solid-state physics and electronics, it generates light. Light emitting diodes and organic light emitting diodes pose several advantages over the current lighting technology but they still require development and research for using them to their full potential. In this paper the characteristics, sources of uncertainty, and market status of light emitting diode are reviewed to provide more suitable research directions for advancement in the field of solid-state lighting. Challenges faced by Light emitting diodes for maintaining color and visual comfort are also illustrated. Failure modes and environmental impact of light emitting diodes are also analysed. Quantum dot based solid state lightening is also presented to study the chromatic characteristics.  Some critical factors of concern for broader application of light emitting diodes and additional enhancements in electrical, optical, temperature characteristic, high power output and color furnishing capabilities are also demonstrated in paper. Light emitting diodes wattage output and efficiency are also discussed for practical viability of solid state devices in emerging fields. The extension lead of current LED technology in evolving applications are considered as accumulation of numerous technologies such as wireless, communication, sensors and control engineering. Undoubtedly, LED engineering is contemporary and the price maybe unreasonable. Nevertheless, it will find its usage in very nearly all applications and the initiation of new techniques that might lessen the cost

Sensor Fabrication Method for in Situ Temperature and Humidity Monitoring of Light Emitting Diodes

In this work micro temperature and humidity sensors are fabricated to measure the junction temperature and humidity of light emitting diodes (LED). The junction temperature is frequently measured using thermal resistance measurement technology. The weakness of this method is that the timing of data capture is not regulated by any standard. This investigation develops a device that can stably and continually measure temperature and humidity. The device is light-weight and can monitor junction temperature and humidity in real time. Using micro-electro-mechanical systems (MEMS), this study minimizes the size of the micro temperature and humidity sensors, which are constructed on a stainless steel foil substrate (40 μm-thick SS-304). The micro temperature and humidity sensors can be fixed between the LED chip and frame. The sensitivities of the micro temperature and humidity sensors are 0.06 ± 0.005 (Ω/°C) and 0.033 pF/%RH, respectively

Perovskite light-emitting diodes

Abstract. The usage of artificial lighting and displays is increasing all the time. Energy efficient and affordable light-emitting materials are being developed widely. Light-emitting diodes (LEDs) are energy efficient, and LED technology and displays based on LEDs have developed greatly in the recent years. In the year 2014, the first research article related to a perovskite LED (PeLED) that is functional in room temperature was released. The light-emitting material in PeLED has ABX3 stoichiometry and perovskite structure. The most common A-cations used in perovskites in PeLEDs are methylammonium, formamidinium and cesium (Cs+). The most common B-cation is lead (Pb2+) and X-anion is a halide or a mixture of halides. Lead halide perovskites are interesting light-emitting materials, since they can be readily solution processed with inexpensive methods. The emission of lead halide perovskites can be tuned across the whole visible spectrum by changing the composition, and the emission colors are bright due to narrow emission. There are multiple challenges in PeLED development. Especially the efficiency of blue PeLEDs needs to be improved. Furthermore, there are challenges related to health and stability. The perovskite used in PeLEDs contains lead, which is poisonous, and perovskites are often solution processed from toxic solvents such as dimethylformamide. The biggest challenges in perovskite stability are sensitivity to moisture, oxygen, illumination and heat. Moreover, the stability is affected by mechanical stress, reactions caused by electric bias and reactions between materials used in PeLEDs. In this thesis, the most common perovskite materials, PeLED architectures, and their characterizations are introduced. Challenges in PeLED development are discussed, especially stability. Perovskite stability can be increased by e.g. perovskite substitution, additives, morphology control and optimization of PeLED structure.Tiivistelmä. Keinovalaistuksen ja näyttöjen määrä kasvaa maailmassa jatkuvasti. Energiatehokkaita ja edullisia valoa emittoivia materiaaleja kehitetään paljon. Valoa emittoivat diodit (light-emitting diode, LED) ovat energiatehokkaita, ja erilaiset LED teknologiat ja niihin perustuvat näytöt ovatkin kehittyneet lähivuosina nopeasti. Vuonna 2014 julkaistiin ensimmäinen tutkimus huoneenlämmössä toimivasta perovskiitti LED:sta (PeLED). PeLED:n valoa emittoivalla materiaalilla on ABX3 koostumus ja perovskiitin kiderakenne. PeLED:ssa käytettävissä perovskiiteissa yleisimmät A-kationit ovat metyyliammonium, formamidinium ja cesium (Cs+). Yleisin B-kationi on lyijy (Pb2+) ja X-anionina käytetään halidia tai niiden seosta (Cl−, Br−, tai I−). Lyijyhalidi-perovskiitit ovat erityisen kiinnostavia materiaaleja, sillä niitä voidaan valmistaa liuoksista edullisesti ja helposti. Lyijyhalidi-perovskiittien emissiota voidaan säätää koko näkyvän valon aallonpituusalueella muuttamalla niiden koostumusta, ja niiden kapea emissiospektri mahdollistaa kirkkaat värit. PeLED:en kehityksessä on vielä lukuisia haasteita. Erityisesti sinisten PeLED:en hyötysuhde vaatii vielä kehittämistä. Lisäksi haasteina on mm. terveysriskit ja stabiilisuus. PeLED:t sisältävät myrkyllistä lyijyä ja niiden valmistuksessa käytetään myrkyllisiä liuottimia, kuten dimetyyliformamidia. Suurimmat haasteet stabiilisuudessa ovat herkkyys kosteudelle, hapelle, valolle ja lämmölle. Lisäksi stabiilisuuteen vaikuttaa mekaaninen rasitus, sähkövirran aiheuttamat reaktiot ja PeLED:ssa käytettyjen materiaalien keskinäiset reaktiot. Tässä tutkielmassa esitellään yleisesti PeLED:ssa käytettäviä perovskiittimateriaaleja, yleisiä PeLED:en rakenteita ja niiden karakterisointia. Lisäksi tutkielmassa perehdytään PeLED:en kehityksen haasteisiin, erityisesti stabiilisuuteen. Perovskiittien stabiilisuutta voidaan parantaa esimerkiksi vaihtamalla perovskiitin koostumusta, käyttämällä lisäaineita, muokkaamalla perovskiittikerroksen morfologiaa ja optimoimalla PeLED:n rakenne