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Visible Light Communication is an emerging technology in Optical Wireless Communication where the Light Emitting Diodes (LEDs) are utilized for transmission of data. The luminance of the LEDs increases with the forward current; however, for high current levels the heat generated by non-radiative recombination of carriers increases the LED junction temperature, decreasing the efficiency and the lifetime...
The development of automotive lighting systems with high illumination quality and high reliability is essential for driving safe and comfort. LEDs have many superiorities over the traditional light sources, such as high reliability, good color quality, long lifetime, energy and space saving, environment friendly and so on, when they are operated under an effective health management (such as thermal,...
Thermal feature is an important factor of LED. However, as an internal parameter, junction temperature cannot be measured easily. Based on the LED circuit model, which is an ideal diode and a resistor in series, a new model of LED junction temperature Tj is proposed in this paper. Parameters can be extracted from the oil bath experiments. In this way, junction temperature can be derived. The accuracy...
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...
The junction operating temperature of a power LED can be estimated by measuring with a thermocouple the temperature of the closest accessible metal part of the LED package, which is in most of the cases one of the electrical terminals, and making a calculation by taking into consideration the thermal resistances of the materials included in the LED structure. In the situations where the electrical...
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...
This paper brings a brief review of LED parameters that can be changed during the life of these types of light sources. Firstly the change of quantitative parameter of emitted light is presented (luminous flux) and following part is dedicated to change of quality parameter (spectral distribution) and change of electrical parameters. Modification of these parameters may affect the use of LEDs in lighting...
In recent years, the use of the electrical test method (ETM) has become more common to measure the temperature of semiconductor junctions. This method makes use of correlating the relationship of the semiconductor forward voltage to the temperature of the device, which is often linear but is always a unique correlation. This method has been recognized by JEDEC, and in particular for LEDs in 2012 when...
Operating junction temperature of LEDs is linked directly to lifetime, long term reliability and failure modes of LED luminaires. It is important to measure the operating junction temperature to assess the health of a LED luminaire / solid state lighting product. Measuring the junction temperature of LEDs is a difficult task as in modern LED luminaires the tiny LEDs are surrounded by optical system...
Junction temperature is a critical parameter for light emitting diode (LED) lifetime and performance estimation. However, it is hard to obtain the junction temperatures in multiple LEDs packaging. In this paper, a estimation method for junction temperatures of multiple LEDs packaging was presented. The method based on an analytical model, and temperature of a point at the substrate surface should...
Die attach process plays a key role in the thermal management of high power LED packages by governing the thermal resistance of the solder interfaces between the LED chips and the substrate materials. In this paper, comparison was made between the GaN based flip chip LED packages fabricated by (1) heated collet and (2) flux reflow eutectic die attach process. Thermal transient characteristics of the...
Thermal resistance of high power blue Light Emitting Diode (LED) package is experimentally examined. The LED package consists of eight CREE EZ900 chips. The dimension of each chip is 880 µm×880 µm and the metal board area is 30 mm×32 mm with 3 mm thickness. The LED package is operated at the current of 11 A with 10 % duty cycle. To measure junction temperature, the forward voltage method is used....
A silicon heat sink with grooved mirror was fabricated by micro-processing technology, then a 5W blue 2×2 LED array with Silicon-based heat sink was accomplished by way of studying its heat conduction. Firstly, the optical ray trace simulation of the array was carried out to study the relationship between light profile and lens shaped, groove height. Then according to the optical simulation results,...
Proper heat management in solid state lighting (SSL) is vital to enhance its efficiency and reliability. The ease of heat flow through the LED package was described in terms of the thermal resistance, Rth. In this study white and green LEDs were used to investigate the variation in junction temperature and junction-to-ambient thermal resistance, RthJA. It was reported that the green LED always shows...
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...
A novel CNT/SiC/epoxy composite was proposed and demonstrated as adhesive joining element and heat dissipation media for HB-LEDs. Junction temperature, luminous intensity and forward voltage were measured for varied combinations in the composites. The experimental results showed that the epoxy with 30 wt% of SiC and 5 wt% of MWCNTs had the best thermal properties. Comparing to commercial epoxy, the...
Flip chip technology is one of the advanced chip packaging techniques in IC packaging industry. This technology may provide a solution to enhancing heat-dissipation and optical performance of the LED when applying to the LED packaging. The goal of this study is to experimentally and numerically study the thermal performance of flip-chip (FC) LED (with the size of 1 × 1 mm) with and without underfills,...
In this paper, we present a PC-based automatic measurement system for measuring the junction temperatures of light-emitting diodes (LEDs) operated at different forward currents. This system is described in three major parts: (1) screen panel and function design of control software (2) data acquisition and heating hardware (3) system integration and function test. In order to check and demonstrate...
The measurements of junction temperature rise and thermal resistance of power LEDs by junction characteristic are proposed in this paper. The measured thermal resistance is corrected by the light-absorbing method. It is also proved that the physical meaning of the electrical average temperature rise of series LED array system is the arithmetic mean of the temperature rise of all sub-LEDs in the system...
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