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This paper discuses on the practical example the problem of thermal modelling of power LEDs used in luminaries. The proper determination of the thermal resistance is crucial for accurate computation of the device junction temperature, which determines the device operating parameters. Here, this problem is illustrated based on the analysis of power LED heating curve measurements taken for various amount...
Thermal resistance and temperature distribution for high-power AlGaInN LED chip-on-board arrays in blue and white versions were measured by different methods and tools. The p-n junction temperature was determined through measuring a temperature-dependent forward voltage drop on the p-n junction, at a low measuring current after applying a high heating current. Furthermore, the infrared thermal imaging...
This work deals with an overall concept of a 3D-stack enabling to produce a directly pluggable high voltage power LED. Using a dedicated silicon vehicle test, a thermal study is carried out with an extensive thermal modelling, optimization, assembly process and Infrared thermal characterization. It is shown that the main thermal issues are due to the presence of the flip chip interconnection layer...
Modulation method and the device for thermal impedance measuring of power COB LEDs and measurement results are described. The measurements were performed by generic modulation method that implies heating a device under test by power varying harmonically. A pulse sequence of heating current, with the pulse length varying harmonically, is passed through the device under test. The p-n junction temperature...
Light-emitting diode (LED) technology has been rapidly developing due to high energy efficiency and longer lifetimes of LED luminaires. One of the main challenges in designing LED components is to manage the inter-twined relation between thermal, electrical, and optical performances. These dependencies are required to be well understood in order to operate LEDs efficiently and have accurate performance...
The driving current, chip area of high-power AlGaInN light emitting diodes (LEDs) and the level of integration of LED arrays are continuously increased to provide ever higher output light flux. The new developments require more attention to pay to the thermal management of LEDs, commonly assessed in terms of the thermal resistance. Temperature distribution in a LED array and its effect on the chip...
A method for determining the thermal resistance of high power LEDs is described. Unlike more complicated systems, this method simply uses a fast pulse to determine the junction temperature under actual operating currents, combined with a conventional thermocouple to measure the mounting face temperature. The literature can be somewhat confusing in describing the thermal resistance of an LED. Often...
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...
Highly stress tests were carried out for GaN-based high power white LEDs with different structures, including traditional lateral, vertical as well as flip-chip LEDs. During the tests, all the electrical, optical and thermal properties were measured in-situ for each LED. The results show that for lateral LEDs, the structure property of LED epitaxial layer is still the key factor that influences the...
Low power surface-mounted (SMD) LEDs are paid much attention in research and development due to their portability and miniaturization. Optical characteristics of SMD LEDs have to maintain more accurate specifications in signaling applications such as traffic lights or railway. Current and temperature stabilization is important for attaining constant spectral properties of SMD LEDs. In this manuscript,...
Investigations in this work are connected with the design and thermal management of LED lamp with spectral characteristics suitable for dairy barns. Spectral power distribution (SPD), optimal for dairy cows is achieved by combinations of LEDs with different spectral characteristics and the control of the LEDs' operation. The thermal management theoretical calculations and the heat sink choice are...
High-power LEDs have many advantages for use in lighting systems. To benefit from these advantages we need to ensure proper heat management. In this paper forward voltage variation is studied as a function of ambient temperature variation at the same supply current. The aim of the study is to estimate the junction temperature as a function of ambient temperature and forward voltage. Two types of LEDs...
Paper presents the static model of the LED behaviour under specific operational conditions created in Simulink tool. This model can be used for different types of LEDs and it operates with commonly available data provided by the manufacturers. Verification of model validity has been performed with high-power white LEDs at two testing methods. First method is based on LED operation with constant supply...
Until now, there has not yet been a standardized method for the LED module thermal resistance measurements. This directly affects the lifetime assessment of the LED modules. By testing and studying the temperature coefficient of the LED modules with different structures, it is found that the temperature coefficient of the LED module follows a linear relationship with voltage when an appropriate test...
In recent years, Light emitting diodes (LEDs) has become more and more popular because of their low power consumption, low-pollution and long-life. Currently, the common lumen maintenance test of LED follows IES LM80-08 standard, which costs at least 6000 hours for measurement and prolongs the time-to-market schedule. In our previous researches, a modified accelerated aging test algorithm using different...
The understanding of the interrelationships among the photometrical, electrical and thermal (photo-electro-thermal) parameters is extremely important to design lighting systems based on light-emitting diodes (LEDs). This paper proposes an improvement in the estimation of the luminous flux previously proposed in A General Photo-Electro-Thermal Theory (PET Theory), using information taken only from...
Recent advancement in solid state technology has made LED lighting energy-efficient and today it is one of the rapidly-developing lighting technologies. Design of LED lighting luminaires is still repeatedly governed by misinterpretations and inappropriate use of the related solid state lighting technology. Heat is generated as byproduct of the light generation process at the LED junction; this heat...
This paper presents two methods for the efficiency measurement of a white light emitting diode (LED) without optical sensors for measuring light intensity. The proposed methods are based on the measurement of the power loss of a white LED. Because all the power loss of a white LED is transferred into heat, it is possible to evaluate the power loss by measuring the temperature of the heat sink attached...
High junction temperature in the LEDs would lead to the reliability problems, such as low quantum efficiency, wavelength shifts, short lifetime, and even catastrophic failure. The effects of various parameters, such as thermal properties of substrates, thermal interface materials (TIM) and heat sinks on the thermal performance of the LED backlight module are investigated experimentally and numerically...
An innovative sensitive test method is developed to detect solder joint cracking for high power LED packages. The method is based on transient thermal analysis and can replace the dominating Light-On test. Test groups of LED packages were soldered with two different lead free solders (SnAgCu 305 and Innolot FL-640) on Aluminum Insulated Metal Substrate and exposed to temperature cycles. Transient...
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