Study of LED thermal properties

Pao Yue-kong Library Electronic Theses Database

Study of LED thermal properties


Author: Tsui, Chi Kin
Title: Study of LED thermal properties
Degree: M.Eng.
Year: 2012
Subject: Light emitting diodes -- Thermal properties.
Light emitting diodes -- Energy consumption.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: viii, 128 leaves : ill. (chiefly col.) ; 30 cm.
Language: English
Abstract: Light is inseparable from human lives. It supports activities at different categories like food & beverage, general lighting, etc. However, it converts a large proportion of electrical power into heat or temperature, which is a waste of energy. Especially for new developing lamps, high energy loss occurs and thus, weakens the expected performance. Therefore, heat removal devices are produced to reduce power consumption and soften energy loss problem. In this project, luminous efficacy of LED lamp is investigated with respect to change in junction temperature. Experimental method was adopted to give technical and statistical supports on the relationship of LED chip's efficacy and its junction temperature. During the tests, LED chip was designed to be used with heat sinks and external fan. A permutation of three heat sinks and one mechanical fan generated six configurations for the experiments. LED chip was mounted on heat sink and, in some scenarios, connected with external fan to provide additional heat rejection effort. After the tests, results were summarized and expressing in graphical format. From the results, it could be seen that luminous efficacy decreased rapidly at high junction temperature. If a heat sink was solely connected to the LED chip, the situation was worsening as well. Junction temperature might exceed an allowable level, resulting in undesirable damage to the p-n structures. In this case, mechanical ventilation was a good support to remove excessive heat from the LED body and was targeting to improve the efficiency. Based on the experimental results, efficacy attended the best value among six scenarios when the LED lamp operated with large-size heat sink and external fan. In this study, it can be concluded that the luminous efficacy of LED chip has an inverse relationship with junction temperature. It should be improved by external effort (both the heat sink and external fan) to maintain acceptable performance. Although there were some limitations to make precise connection between luminous efficacy and junction temperature within a single equation, the obtained statistical results provided sufficient evidence to comment LED lamp's thermal property.

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