LED Life Research Articles

Multi-Stress Accelerated Degradation Testing Reliability Assessment of LED Lamp Beads Considering Generalized Coupling

Due to the complex operating environment of LED lamp beads (hereinafter referred to as LED), the test method that only considers the action of multiple stresses alone ignores the mutual influence between stresses, making it difficult to accurately obtain the life indicators of LEDs, resulting in a large deviation in the theoretical life results. In this regard, this paper proposes a multi-stress accelerated degradation evaluation method considering generalized coupling and conducts an accelerated degradation test (ADT) to evaluate the life of LEDs. We identified three stress sources and designed five new high-gradient ADTs. Through experimental data, we found that the three stress sources are strongly coupled on this LED. Then, a generalized coupling maximum likelihood estimation method (MLE) for the entire sample was constructed, and the particle swarm algorithm was used to solve the parameters. Finally, the life of this LED was evaluated based on the experimental data. The results show that the life of the LED considering multiple-stress coupling is within 6.5% of the historical life scatter point, which is more in line with the actual working environment.

Operation of Electronic Devices for Controlling Led Light Sources When the Environment Temperature Changes

Ambient temperature significantly affects the electrical and light parameters of LEDs, such as forward and reverse current, voltage drop LEDs and luminous flux. With an increase in temperature, the decrease in the intensity of LED radiation is explained by physical processes, including the phenomena of non-radiative recombination due to impurity levels, recombination on the surface, losses carriers in the barrier layers of heterostructures, etc. The increase in temperature is also significantly reduces the useful life of LEDs and the LED device in general. Drivers, which allows to stabilize the operating current with a change in the supply voltage of the device and, as the result is light flux. But in LEDs of various types, current stabilization does not lead to the stabilization of the light flux when the temperature regime of their operation changes. When changing ambient temperature in the range of +40…+60 °C, the luminous flux of LEDs is significant decreases even in the case when their current is kept constant, as we can see from documentation for most of LED types. An article analyzes the effect of temperature on electrical and light parameters LEDs with different types of drivers as part of LED lighting devices, such as LED lamps and LED spotlights, in order to offer possible constructive solutions for partial reduction or elimination of the decline problem luminous flux of LED devices under conditions of their operation at high temperatures.

An improved LED junction temperature test method based on FCM

High junction temperature (Tj) of LED will affect the performance and life of LED, so this paper proposes a high-power LED junction temperature test method. Mainly aiming at the problem that the accuracy of the forward current method (FCM) will be affected by the calibration procedure, equipment aging, and technical differences when batch testing LED Tj, this paper uses the relationship between relative current and Tj to calibrate the procedure based on this method, to limit the negative affection of sample heterogeneity. Ten LED samples were tested in the experiment, and the Tj errors under two test methods were obtained. The results showed that the improved method was more accurate than the traditional method. Then, the Tj error of the improved method was compared with that of the forward voltage method, and the error of the new method was smaller.

Color Offset in the Process of High-Power LED Life Aging

In order to study color offset of the high-power white light and blue light LED in the whole life, a series of high-power white light and blue light emitting diodes are lighted continuously under a constant current. In the light of different period of time, measured the light emitting diode emission spectrum, color coordinate, color temperature of the light emitting diodes are measured at different periods; light luminous flux, color coordinate and color temperature changes are also measured under different currents. The experimental results show that the color of LED is different at different period under the same current, and is also different under a variable current. The article studied the influence of different factors on the color offset, and pointed out that the high-power LED color offset is caused by not only phosphors aging but also more major changes of the material itself. Furthermore, the results will provide a reference to the application of white LED and for the further study.

Preparation and Properties of SiC/Phenolic Resin for the Heat of LED

In order to solve the problem that low thermal conductivity of the plastics for the heat of LED, SiC/Phenolic resin for the heat of LED were fabricated combining powder metallurgy. The effects of particles diameters, content and adding nanoparticles on thermal conductivity of the fabricated composites were investigated, the mechanical properties were also characterized. The experimental results showed that the materials were obtained, and the insulation performance of the fabricated SiC/Phenolic resin was higher than the industry standard one, the thermal conductivity reached 4.1W/(m·k)-1. And the bending strength of the fabricated composites was up to 68.11MPa. The problem of low thermal conductivity of the material is expected to be solved. In addition, it is meaningful for improving LED life.

A Life Prediction Model for LEDs Lamps Based on the Thermal Life Theory

The photometric, electrical, thermal and life features of LEDs are highly dependent on each other. All these factors should be considered together in order to optimize the operating point of LEDs. A thermal life theory about LEDs is developed. This theory shows the inner inks among photometric thermal and 1ife features of a LED. A life prediction model of LEDs and the relationship between output luminous flux and lifetime was found out by this theory. The life of LEDs can be predicted and find the proper operating point, at which the LED will generate the maximum amount of luminous flux in its total life cycle.

Test Systems for Life of LED Light Based on Junction Temperature

In order to predict the life of white LED in a short time, three groups constant stress accelerated life tests were conducted by increasing the working current. Life information of LEDs was obtained by using bilinear regression method. The numerical results indicated that the scheme of the accelerated life tests was correct and feasible. The estimation of the LED life was accurate by acceleration parameters．

Methodology of reliability enhancement for high power LED driver

The degradation of a linear-mode high power LED driver is studied. This driver is to provide constant current to LED regardless of its output voltage, but there is a minimum output voltage whereby the output current cannot be maintained as constant. Prolonged operation of the driver through relevant reliability test revealed that this minimum voltage will increase due to degradation of the output transistor in the driver, and when this minimum voltage exceeds the operating voltage of the driver, it no longer provides a constant current to the LEDs. Our investigation clearly reveals that the degradation mechanism is hot carrier injection as will be shown in this work, and hence it is inevitable. As high power LEDs have long life time, their drivers must also have equivalent lifetime so that the long life of LEDs can be leveraged in the entire luminary. One method to enhance its lifetime is to increase the hot carrier injection lifetime of the output transistor which may requires some fundamental change in the transistor structure and/or processing, and it is beyond the control of the driver designer and can be expensive also. A circuit approach is to use redundant circuit for enhancement which is common in the circuit world. Effective switch over to redundant circuit requires continuous health monitor of the primary circuit. In this work, the method to identify the health monitoring index, based on the degradation mechanism is shown, and the control circuit to detect and switch over to the redundant circuit is also designed and presented here.

PENDETEKSI KETINGGIAN LEVEL AIR DENGAN TAMPILAN LCD BERBASIS MIKROKONTROLLER ATMEGA 8 SERTA LED BUZZER DAN SEVEN SEGMENT SEBAGAI PERINGATAN DINI KENAIKAN AIR PASANG (ROB) BERBASIS PROGRAMMABLE LOGIC CONTROLLER CP1E-E40DR-A

Rizal Fauzan Adi Rahardjo, Heru Winarno, in paper water level detection based atmega 8 microcontroller with lcd display, led, buzzer and seven segment as early warning of post water (rob) increase based CP1E-E40DR-A programmable logic controller explain that as a result of the overflow of the tidal sea water in rural areas sriwulan sayung District of Demak , the tidal water easily entered into the residential area , which can be fatal if not in further tackle. Tidal flood has become commonplace in the area Sriwulan Sayung District of Demak . However , the longer the tidal flood is troubling and very disturbing society . So I took the initiative to create a miniature tidal flood prevention . Height of the water level of a river that flows directly into the sea will be detected by the sensor. The sensors will send data to the PLC and will be displayed by the seven segment . Further increase in the water level of the river will also affect the water level in the ditch homes residents . Height of the ditch water level is detected by the sensor which will send data to the PLC and then displayed by seven segment LCD and previously through the microcontroller atmega 8. The maximum height of the water level gutter will be marked with berbunyinya buzzer and LED life. Keywords : Sensor , Seven Segment , Microcontroller Atmega 8 , LCD , LED, buzzer.

Analysis and Prediction of Thermal Resistance for High Power LED Using GA-SVR

With the development of high power LED technology, junction temperature as a key factor constrains the performance and the service life of LED, and the main parameter of junction temperature is thermal resistance. Therefore, how to measure the thermal resistance of high power LED quickly and accurately plays an important part in improving the performance and the service life of LED. In this paper the accurate and fast measurement equipment was applied to study the thermal characteristics of high power LED. The forward-voltage based method was conducted to measure the junction temperature of high power. Then, support vector regression (SVR) combined with genetic algorithm (GA) for its parameter optimization, was proposed to establish a model to predict the thermal resistance of high power LED. The prediction performance of GA-SVR was compared with those of BPNN model. The result demonstrated that the estimated errors GA-SVR models, such as Mean Absolute Relative Error (MARE) and Root Mean Squared Errors (RMSE), all are smaller than those achieved by the BPNN applying identical samples.

Experimental and simulation studies on useful life of low power LED illumination sources

This paper reports experimental and simulation studies on degradation of optical power of low power LEDs due to current stress and temperature variation. The goal of this study was to study the effect of aging and ambient temperature on optical output power of light emitting diodes and to determine the effective life span of LED under stress condition. The LED samples were stressed at four levels of operating current (recommended current 20 mA) 20 mA, 30 mA, 40 mA, and 45 mA with stress time up to 1000 h. We find that degradation rate increases with increasing operating current. When LEDs are overstressed by driving at higher current the optical power degraded with stress time. A Mathematical model is developed to predict the behavior of LED at different operating current. Simulations are carried out with this model using MATLAB. Using degradation pattern at higher operating current the life span of these LEDs was predicted at normal operating current. To verify the simulation results we have used LED life data from different research papers. The authors believe that the model is useful for predicting working life of AlGaInP /AlGaAs / GaAs / GaInN / InGaAsP / InP LED.

Flow and heat transfer in porous micro heat sink for thermal management of high power LEDs

A novel porous micro heat sink system is presented for thermal management of high power LEDs, which has high heat transport capability. The operational principle and heat transfer characteristics of porous micro heat sink are analyzed. Numerical model for the micro heat sink is developed to describe liquid flow and heat transfer based on the local thermal equilibrium of porous media, and it is solved with SIMPLE algorithm. The numerical results show that the heated surface temperature of porous micro heat sink is low at high heat fluxes and is much less than the bearable temperature level of LED chips. The heat transfer coefficient of heat sink is very high, and increasing the liquid velocity can enhance the average heat transfer coefficient. The overall pressure loss of heat sink system increases with the increasing the inlet velocity, but the overall pressure drop is much less than the pumping pressure provided by micro pump. The micro heat sink has good performance for thermal management of high power LEDs, and it can improve the reliability and life of LEDs.