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

An application of Dijkstra’s algorithm model in finding shortest travel time in KLCC

Nowadays, traffic congestion or also known as traffic jammed is one of the common routing problems that usually occur on road networks. Routing problems becomes one of the big concern that most of the develop country must face including Malaysia

Thermal Characterization and Lifetime Prediction of LED Boards for SSL Lamp

This work presents a detailed 3-D thermo-mechanical modelling of two LED board technologies to compare their performance. LED board are considered to be used in high power 800 lumen retrofit SSL (Solid State Lighting) lamp. Thermal, mechanical and life time properties are evaluated by numerical modelling. Experimental results measured on fabricated LED board samples are compared to calculated data. Main role of LED board in SSL lamp is to transport heat from LED die to a heat sink and keep the thermal stresses in all layers as low as possible. The work focuses on improving of new LED board thermal management. Moreover, reliability and lifetime of LED board has been inspected by numerical calculation and validated by experiment. Thermally induced stress has been studied for wide temperature range that can affect the LED boards (-40 to +125°C). Numerical modelling of thermal performance, thermal stress distribution and lifetime has been carried out with ANSYS structural analysis where temperature dependent stress-strain material properties have been taken into account. The objective of this study is to improve not only the thermal performance of new LED board, but also identification of potential problems from mechanical fatigue point of view. Accelerated lifetime testing (e.g., mechanical) is carried out in order to study the failure behaviour of current and newly developed LED board

Color Point Tuning for (Sr,Ca,Ba) Si2O2N2:Eu2+ for White Light LEDs

Color point tuning is an important challenge for improving white light LEDs. In this paper, the possibilities of color tuning with the efficient LED phosphor Sr1−x−y−zCaxBaySi2O2N2:Euz2+ (0 ≤ x, y ≤ 1; 0.005 ≤ z ≤ 0.16) are investigated. The emission color can be tuned in two ways: by changing Eu2+ concentration and by substitution of the host lattice cation Sr2+ by either Ca2+ or Ba2+. The variation in the Eu2+ concentration shows a red shift of the emission upon increasing the Eu concentration above 2%. The red shift is explained by energy migration and energy transfer to Eu2+ ions emitting at longer wavelengths. Along with this (desired) red shift there is an (undesired) lowering of the quantum efficiency and the thermal quenching temperature due to concentration quenching. Partial substitution of Sr2+ by either Ca2+ or Ba2+ also results in a red-shifted Eu2+ emission. For Ca2+ this is expected and the red shift is explained by an increased crystal field splitting for Eu2+ on the (smaller) Ca2+ cation site. For Ba2+, the red shift is surprising. Often, a blue shift of the fd emission is observed in case of substitution of Sr2+ by the larger Ba2+ cation. The Eu2+ emission in the pure BaSi2O2N2 host lattice is indeed blue-shifted. Temperature dependent luminescence measurements show that the quenching temperature drops upon substitution of Sr by Ca, whereas for Ba substitution, the quenching temperature remains high. Color tuning by partial substitution of Sr2+ by Ba2+ is therefore the most promising way to shift the color point of LEDs while retaining the high quantum yield and high luminescence quenching temperature

Luminescent behavior of the K2SiF6:Mn4+ red phosphor at high fluxes and at the microscopic level

Phosphor-converted white light-emitting diodes (LEDs) are becoming increasingly popular for general lighting. The non-rare-earth phosphorK(2)SiF(6): Mn4+, showing promising saturated red d-d-line emission, was investigated. To evaluate the application potential of this phosphor, the luminescence behavior was studied at high excitation intensities and on the microscopic level. The emission shows a sublinear behavior at excitation powers exceeding 40 W/cm(2), caused by ground-state depletion due to the ms range luminescence lifetime. The thermal properties of the luminescence in K2SiF6: Mn4+ were investigated up to 450 K, with thermal quenching only setting in above 400 K. The luminescence lifetime decreases with increasing temperature, even before thermal quenching sets in, which is favorable to counteract the sublinear response at high excitation intensity. A second, faster, decay component emerges above 295 K, which, according to crystal field calculations, is related to a fraction of the Mn4+ ions incorporated on tetragonally deformed lattice sites. A combined investigation of structural and luminescence properties in a scanning electron microscope using energy-dispersive X-ray spectroscopy and cathodoluminescence mappings showed both phosphor degradation at high fluxes and a preferential location of the light outcoupling at irregularities in the crystal facets. The use of K2SiF6: Mn4+ in a remote phosphor configuration is discussed

Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication.

An advanced light-fidelity (Li-Fi) system based on the blue Gallium nitride (GaN) laser diode (LD) with a compact white-light phosphorous diffuser is demonstrated for fusing the indoor white-lighting and visible light communication (VLC). The phosphorous diffuser adhered blue GaN LD broadens luminescent spectrum and diverges beam spot to provide ample functionality including the completeness of Li-Fi feature and the quality of white-lighting. The phosphorous diffuser diverged white-light spot covers a radiant angle up to 120(o) with CIE coordinates of (0.34, 0.37). On the other hand, the degradation on throughput frequency response of the blue LD is mainly attributed to the self-feedback caused by the reflection from the phosphor-air interface. It represents the current state-of-the-art performance on carrying 5.2-Gbit/s orthogonal frequency-division multiplexed 16-quadrature-amplitude modulation (16-QAM OFDM) data with a bit error rate (BER) of 3.1 × 10(-3) over a 60-cm free-space link. This work aims to explore the plausibility of the phosphorous diffuser diverged blue GaN LD for future hybrid white-lighting and VLC systems