Due to their long lifetime and high efficacy, light emitting diodes have the potential to revolutionize the illumination industry. However, self heat and high environmental temperature which will lead to increased junction temperature and degradation due to electrical overstress can shorten the life of the light emitting diode. In this research, a methodology to investigate the degradation of the LED emitter has been proposed. The epoxy lens of the emitter can be modelled using simplified Eyring methods whereas an equation has been proposed for describing the degradation of the LED emitters.@en

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 shift (CS) process of LED products. Consequently, a CS mechanism constant is obtained for detecting the consistency of CS mechanisms among various stress-loaded conditions. A statistical procedure with the proposed power model is then derived for the CS paths of LED lamps in step-loaded stress testing. Two types of commercial LED lamps with different capabilities of heat dissipation (CHDs) are investigated. Results show that the color coordinates of lamps are easily modified in various stress-loaded conditions, and different CHDs of lamps may play a crucial role in the various CS processes. Furthermore, the proposed statistic power model is adequate for the CS process of LED lamps. The consistency of CS mechanisms in step-loaded stress testing can also be detected effectively by applying the proposed statistic procedure with the power model. Moreover, the constant assumption in the model is useful for judging the consistency of CS mechanisms under various stress-loaded conditions.@en

A degradation mechanism analysis methodology is proposed for the mid-power white-light LED packages in this paper. Based on the degradation data obtained from a series of aging tests that are performed on the individual packaging material, the degradation kinetics of lumen output and spectral power distribution of the LED packages are investigated using optical simulation. As a result, although the reflectivity of the packaging materials decreased severely for the blue lights (i.e., 450 nm), the simulation showed that lights at this wavelength were little absorbed in the LED package. More specifically, it is found that: 1) the degradation of the blue lights is mainly due to blue chip deterioration, while rarely affected by the degradation of the silicone encapsulant and other packaging materials; 2) the degradation of the down-converted lights is significantly attributed to the degradation of the blue chips, the phosphors, the lead frames, and the package housing; and 3) the degradation of the silicone encapsulant contributes about 1.35% to the total lumen degradation within 168 h, while has no more contribution to the lumen degradation with further aging duration. The simulation results have been validated by experiments and successfully applied to the degradation mechanism analysis of LED packages in LM-80-08 tests.@en

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO 2 , O 2 , NO, NH 3 , SO 2 and NO 2 ) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO 2 , O 2 , SnSe monolayer performs stronger affinity for SO 2 and NO 2 , which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO 2 , while physically adsorbing SO 2 , is more suitable for the adsorption mode of SO 2 sensors. Surprisingly, the adsorption amount of SO 2 is 6 times that of NO 2 . Therefore, the adsorption of SO 2 is more likely to occur compared to other gas molecules. For a mixed environment of SO 2 and NO 2 , the adsorption quantity of SO 2 is not significantly affected, while the adsorption of NO 2 is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO 2 sensors with high selectivity and sensitivity. @en

In this paper, lumen degradation is described by using a modified Brownian motion process for mid-power white-light LED packages, which were aged under step stress accelerated degradation test (SSADT). First, a SSADT model has been established based on the theory of equivalent accumulative damage. Then, a method was proposed to improve the accuracy of the parameter estimation by carefully modifying the estimator, which was proposed in the previous research. Experimental data show that parameters estimated by using SSADT model are very close to those estimated by using constant stress accelerated degradation test (CSADT) model, indicating the feasibility of the SSADT model. The experiment also indicates that SSADT can be used as an alternative to CSADT, as it enables comparable estimation accuracy, while using less testing time, a smaller sample size and less test capacity.@en

This paper presents our effort to predict the system reliability of Solid State Lighting (SSL) applications. A SSL system is composed of a LED engine with micro-electronic driver(s) that supplies power to the optic design. Knowledge of system level reliability is not only a challenging scientific exercise but it is also crucial for successful adoption of future SSL systems. Currently, the lifetime of a SSL system provided by the manufacturers is often based on just the life time of the LED emitter but a malfunction of the system in reality is often induced by the failure or degradation of a combination of subsystems/interfaces. Hence, a significant improvement in the future SSL system can be achieved when the system level reliability is well understood by proper experimental and simulation techniques.@en

Although color shift is one of the key issues to be considered for the failure of LEDs products, there is limited literature that correlated LED products' lifetime performance to their color shift over time. This is mainly due to the lack of a suitable model to define the color shift over time. In this paper, a methodology for characterizing and predicting the color shift of the polycarbonate materials in LED products is developed. It had shown that the color shift follows the 1st order reaction. Furthermore, the rate coefficient k of the reaction was found to follow Arrhenius relationship with activation energy of 0.046eV.@en

Lumen depreciation is one of the major failure modes in light-emitting diode (LED) systems. It originated from the degradation of the different components within the package, being the LED device or chip, the driver, and the optical materials (including phosphorous layer). This chapter describes the state of the art of the degradation mechanism for these components and how they contribute to the lumen depreciation of the LED package as a whole.@en

IGBT device is developed from silicon to wide bandgap semiconductor materials, and its working temperature has reached to 300 °C, so the encapsulation is particularly important. NanoCu paste is investigated under H2 at 300°C. A chip is linked to DBC substrate by nanoCu paste under air with different temperature. Results shows the increase of sintered time temperature effectively reduce the porosity of sintered layer and enhance the strength.@en

We report a molecular modelling study to validate the forcefields [condensed-phase optimised molecular potentials for atomistic simulation studies (COMPASS) and polymer-consistent forcefield (PCFF)] in predicting the physical and thermophysical properties of polymers. This work comprises of two key steps: (1) generating and validating the molecular model in predicting the material properties of the bulk amorphous emeraldine base polyaniline and (2) modelling the glass-rubber transition of the polymer. From all the molecular dynamics simulation results, it clearly shows that the more recent COMPASS forcefield provides a higher accuracy in predicting the polymer properties than PCFF and it enables a more accurate prediction of condensed-phase properties (density, glass transition temperature, solubility parameters, etc.) in a broad range of temperature for various applications.@en

Due to their long lifetime and high efficacy, solid state lighting (SSL) has the potential to revolutionize the illumination industry. The long lifetime claimed by the manufacturers is often based solely on the estimated depreciation of lumen for a single LED operating at 25°C. However, self heating and high environmental temperature which will lead to increased junction temperature and degradation due to electrical overstress can shorten the life of light emitting diode. Furthermore, each SSL system includes different components such as the optical part, electrical driver and interconnections. The failure/degradation of any components wills severely affects the performance and reliability of whole system and hence the weakest component will become the bottleneck for the reliability and lifetime of the module. Literature reviews of the factors influencing the life of LED lamps identified the degradation of the epoxy lens and plastic package due to the junction temperature and voltages as one of the common failure mode. In this research, a methodology to predict the degradation of the epoxy lens has been proposed. In order to correlate the mean time to failure as a function of the junction temperature and the inputted voltage, the simplified Eyring models had been proposed in this research. Since the life of a SSL system is subjected to varying loading condition, another objectives of this research is to present a methodology to predict the life of a SSL under changing condition.@en

Solid state lighting (SSL) is a new lighting technology based on high brightness light emitting diodes (LED). This technology because of being much more energy efficient, having longer lifetime and design flexibility has attracted the attention of both manufacturers and consumers. This technology looks very promising because of its advantages with respect to conventional lighting systems. Especially for some applications like outdoor lighting and automotive applications, using SSL can be very beneficial. Nevertheless there is still requirement to study about the reliability and performance of these lighting systems in different environments [1]. Each SSL lighting system is constructed by two major parts; optical part and electrical driver. The effect of temperature on performance and reliability of SSL system electrical driver is the focus of this research. In the beginning we will discuss about the fundamental SSL electronic driver building blocks; control/information, switching and electromagnetic energy storage. It will be explained that the last two blocks, switching and electromagnetic energy storage, are the heart of power conversion and thus more sensitive to the temperature. In this paper we focus on electromagnetic energy storage part. Ceramic capacitors are the most commonly used devices as electromagnetic energy storage component in SSL drivers. Thermal studies generally focus on steady state temperature dependency of the devices and they ignore the transient part of the temperature variation. Although in applications like automotive SSL lighting and also outdoor lighting the transient part of the temperature change should be also taken into account. In this paper we show that the transient part of the temperature change can also play an important role in performance of the most common type of the electromagnetic storage part of an SSL driver.@en

Solid State Lighting (SSL) technologies and products are gradually pervading into our daily life. A SSL system is composed of a LED engine with a micro-electronics driver(s), integrated in a housing that also provides the optical, sensing and other functions. Knowledge of system level reliability is crucial for not only the business success of the future SSL applications, but also solving many associated scientific challenges. In practice, a malfunction of the system might be induced by the failure and/or degradation of the subsystems/interfaces. Extra costs, in terms of additional efforts/designs/parts, have been considered in order to secure the guaranteed reliability performance of SSL system. Most of SSL system designs, which allow few failures of the subsystem/interface during the application period, can be achieved with significant cost reduction when the system level reliability is well understood by proper experimental and simulation techniques. This paper will cover the reliability of total SSL systems including the reliability theories and practices for all (sub-) components, such as LED engines, drivers and fixtures. @en