Research on test method of thermal resistance and junction temperature for LED modules

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 current is applied. In this paper, we investigate the feasibility of measuring the thermal resistance of the LED module as a whole. Furthermore, we propose a method to estimate the junction temperature of the LED module based on the thermal resistances of each of its individual LED and the module itself. This method provides an important basis for the junction temperature calculation in the assessment of the lifetimes of the LED module. However, since the LED module usually has a large surface, the uncertainties existing in the materials and fabricating process will result in a distributed temperature within the LED module. And in most cases, the first failure occurs in the chip with the highest junction temperature. Therefore, the next step of our research will focus on the evaluation of the maximum junction temperature of the LED module based on the proposed method.

1. Introduction

LED modules are widely used in LED lighting products, such as street lamp, tube light, bulb lamp, so the performance of LED module directly affects the reliability of LED lighting products. And LED modules' thermal resistance and junction temperature measurement is the key to the analysis of the LED module thermal performance. At present there is no standard of LED module thermal resistance measurement. As LED module is light-emitting devices, electrical method are usually adopted to measure the thermal resistance. The researchers has proposed junction temperature test method based on thermal resistance matrix of the LED module [1], analysing junction temperature by combining experiment with simulation [2]. There are some articles about taking the module as a whole to measure the thermal resistance of it, but without specific introduction of the testing method [3].