Fundamental study on simplified temperature prediction method for LED

In recent years, LED is attracted attention as new light sources. LED bulb is one of the LED usages and this is a replacement for conventional indoor lighting such as incandescent light bulbs and fluorescent lamps. LED bulbs have advantages such as long life and low power consumption compared to other light sources. However volume of LED chip is small and the amount of heat generation per area is becoming large. That causes degradation of LED chips because of high temperature. Therefore, thermal design is important for LED bulbs and other LED devices. The thermal design of the LED must take into account various parameters, for example thermal conductivity, area and thickness of the substrate of the LED and heat transfer coefficient around the LED. However, there are no guidelines for thermal design of the LED, and reliability of the LED is depending on thermal designers. This work aims to propose a guideline of thermal design of the LED. In this paper, as the first step of the guideline, simple temperature prediction method for the LED was discussed. Thermal network model was employed as the simple method. To verify an appropriate simple temperature prediction method with thermal network model, CFD (Computational Fluid Dynamics) analysis was conducted and important points for making thermal network model are discussed. As a result, it was found that a key point for making a simple temperature prediction model of the LED is how to estimate the heat flow in in-plane direction and thickness plane direction of the substrate simultaneously.