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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...
We demonstrate a novel real-time steam quality measurement system relying on NIR absorption. A simple two-phase flow model is used where the vapor phase absorbance is assumed constant for high steam quality for a given pipe pressure. Two NIR light sources of different peak wavelengths are used to compensate for reflection and scattering. A sensor prototype was designed using high temperature resistant...
Characterization of LEDs and other semiconductor devices demands at least accurate monitoring of the junction temperature (Tj), also its control in more complex cases. In practical LED lighting appliances “hot lumens” are meaningful, as most lamps are used in steady state with power applied. Analysis in cold state provides only indirect information about the intended operation. On the other hand,...
Thermal management is one of the key issues arising in designing light-emitting diode (LED) based luminaire products. Dynamic compact thermal models (DCTMs) are required to predict the thermal behaviour of LED packages fast and accurately in system level simulations. The European Delphi4LED consortium aims to develop multi-domain (electrical-thermal-optical) compact models. One of its targets is to...
Reliability and lifetime of LED modules depend critical from drive current and junction temperature. Transient thermal analysis (TTA) is widely used to measure the transient thermal impedance Zth and the thermal resistance Rth of LEDs to access the junction temperature. To predict the junction temperature of an LED in an application during product design and development calibratedfinite element (FE)...
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...
Light output performance of power LEDs is sensitive to the junction temperature and also changes with the elapsed lifetime of the device. A smart control to achieve constant light output of LED based products would be advantageous in many applications such as streetlighting, resulting e.g. in considerable power savings when forward current is reduced when ambient temperatures are lower. Also, continuous...
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...
The solid lighting industry comply with costumer's requirements of high light output and a higher grade of functionality, especially in the automotive sector. The integration of multiple LED-chips on one illuminant has the advantage of weight and size reduction. However, multiple LED-chips lead to increased power density; to get rid of their produced heat, an energy strategy is necessary. The key...
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...
Rapid growth of Solid-State Lighting market has been supported by progress in Light Emitting Diode (LED) technology. Strong competition requires that lighting product development cycle should be shorter and more effective. Optimal design of a LED luminaire in major degree depends on thermal-electro-optical properties of LEDs in use. These properties are required to be accurately characterized and...
The main objective of the Delphi4LED project (funded by the Ecsel European joint undertaking) is to develop a standardized method to create multidomain LED based design and simulation flow for the solid-state lighting industry. Tools and standards will be developed at various levels to enable design and manufacturing of more reliable and cost effective LED based lighting solutions which can be brought...
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...
In phosphor-converted light-emitting diodes (pc-LEDs), phosphor heating can lead to decrease of luminous efficiency or even thermal quenching due to local high phosphor temperature. Phosphor scattering model has been used to calculate the phosphor heat generation. Using this model, there are two methods for heating power estimation, one is the subtractive method and the other is the integral method...
The silicone has been widely used in the LED packaging process and the dispensing method is commonly implemented to deliver the silicone on the LED chip. In the dispensing process, the consistency of droplet volume can make great effects on the quality of the LED products, such as the optical property and its service life. To improve the consistency of droplet volume, the rheological property of silicone...
In the phosphor coating process of the phosphor-converted light-emitting diodes (pc-LEDs) packaging, the phosphors settle spontaneously due to the density difference between the phosphor particles (YAG-04, about 4800 kg/m3) and the silicone matrix (OE6550 A/B, about 1120 kg/m3). The phosphor sedimentation affects the phosphor distribution and changes the optical performance of pc-LEDs, such as the...
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,...
The paper presents the failure mode of high-power light emitting diodes (LEDs) under mechanical pressure and verifies the bonding wire as the weakest structure of LEDs. Different lens radiuses and heights are studied to demonstrate the influence of lens parameters on the mechanical strength of LEDs. The experimental results have demonstrated that a LED device has a higher failure force when the lens...
Nanowires (NWs) have potential to enable new types of light-emitting diodes (LEDs), which also entail challenges for the development of improved full device simulation models. In this work we calculate the extraction efficiency and emission enhancement in NW array LEDs at different temperatures and couple the results to carrier transport simulations. Our results show that the extraction efficiency...
One of the great advantages of LED based lighting fittings is their efficiency. Efficient cooling solutions are needed even for this type of fittings because of the high power density. This paper presents a comparison between passive cooling, with a heat sink, and active cooling using a fan. This paper discusses how fans can be used to cool high power COBs(chip on board) without significantly increasing...
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