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In order to ensure the exchangeability of LED light engines in LED based luminaires, the Zhaga consortium develops standard specifications for the interfaces of LED light engines. The complete interface definition consists of the description of a mechanical, optical, electrical and thermal interface. The thermal interface has to ensure a good thermal contact between the engine and the fixture. Next...
In this paper we aim at highlighting different aspects of thermal testing of AC LEDs, especially of retrofit LED lamps which are directly driven from the AC mains supply. The main focus is the concept of thermal impedance applied for AC driven LEDs and the AC heating power. The paper gives an overview of the different representations of the thermal impedance then provides estimates of the AC power...
Although critical to the lifetime of LED, the junction temperature of LED cannot be measured easily. From the general photo-electro-thermal theory for LED systems, new equations for estimating the internal junction temperature Tj and junction-case thermal resistance Rjc of LED from the luminous flux measurements, which can be obtained relatively easily, are presented and verified practically. These...
Investigations in this work are connected with design of energy effective multifunctional lamp for interior lighting. A mechanical construction of a desk lamp is used. LEDs are chosen as light sources. Characteristics of LEDs allow creating lightweight construction which can serve as: desk lamp (light flux about 600 ÷ 700 lm); night light for baby room (light flux about 100 ÷ 200 lm) and lamp for...
Investigations deals with optimization of operating regimes of LEDs in lighting equipment for obtaining two purposes - maximum light output in dependence of ambient conditions and long term lumen maintenance. Thermal management calculations and heat sink choice are experimentally tested at various ambient conditions (air temperatures from 20oC to 55oC) and different current values through LEDs - up...
Different high-end white power LEDs from different LED vendors were studied. The aim of the study was to find the optimal choice of LEDs and thermal management solutions for a street-lighting application. The primary concern was the (real) junction-to-heatsink thermal resistance of the LED or LED assembly and the real junction temperature and the actual light output of the individual LEDs under test...
In this paper we investigate what kind of failures are likely to happen in LED based streetlighting luminaires and what are the requirements for being able to detect these by means of thermal transient testing. Based on preliminary results of long term stability studies of LEDs done in cooperation with the Pannon University in Veszprém, Hungary one should expect degradation of different thermal interfaces...
This paper aims at providing a rigorous description of the thermal impedance of AC LEDs, especially of retrofit LED lamps which are directly driven from the mains supply. The paper gives an overview of the different representations of the thermal impedance then provides estimates of the AC power of LEDs for two extreme cases (voltage and current driven situations). The high harmonic content of the...
In this paper, the thermal analysis is carried out by the combination of actual thermal measurement and numerical finite element simulation to investigate insightfully the thermal characteristics of each element in the whole assembly of the LED lighting system (LLS). Based on the thermo/fluid coupled field numerical simulation, the ANSYS??,s finite elements are used to model the detailed assembly...
We studied the thermal properties LED light unit composed of nine LED chips in a MLCMP (multi-layer ceramic-metal package) and compared various thermal dynamic models. We concluded that the direct measurement of forward voltage Vf is the most practical approach for in-situ testing. By calibrating the Vf to junction temperature Tj at various forward current in a temperature controlled oven, the linear...
Nowadays the demand for thermal standards for power LEDs is increasing. On the one hand metrics for fair comparison of competing products are needed; on the other hand, designers of power LED-based applications demand reliable and meaningful data for their daily work. Today's data sheet information does hardly meet any of these requirements. In earlier papers we compared the current situation in the...
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