Measurement of junction-to-ambient thermal resistance of a LED lighting luminaire

Recent advancement in solid state technology has made LED lighting energy-efficient and today it is one of the rapidly-developing lighting technologies. Design of LED lighting luminaires is still repeatedly governed by misinterpretations and inappropriate use of the related solid state lighting technology. Heat is generated as byproduct of the light generation process at the LED junction; this heat needs to be dissipated in an efficient manner. The correct method of thermal management in the LED luminaire is critical for effective heat transfer from the junction to the ambient. Light output, useful life and long term reliability of an LED luminaire are strongly associated with the temperature of the LED junction. Inadequate heat dissipation influences LED life and consequently the long term reliability of the entire LED luminaire. It is therefore important to have the proper knowledge about the light-output and thermal properties of the LED luminaire. This work proposes a methodology for the measurement of the junction-to-ambient thermal resistance of a market ready LED luminaire using the linear relationship between forward voltage and junction temperature of the LEDs. Measurement of the junction-to-ambient thermal resistance of a LED luminaire is essential to assess the quality of the thermal design of the luminaire. Considering two LED luminaire with similar electrical and photometric characteristics, the LED luminaire with lower junction-to-ambient thermal resistance has better heat management system compared to the one with a higher value of the junction-to-ambient thermal resistance. The methodology used in the study and findings of this study are discussed in this paper. If two similar LED luminaires are tested using the proposed method, their thermal management systems can be assessed based on junction-to-ambient thermal resistance.