Comparison of methods for measurement of HP-LEDs based on the junction temperature (Conference Presentation)

High power LEDs (HP-LEDs) are key building blocks of solid-state lighting products, therefore, it is important for LED manufacturers, lamp/luminaire manufactures, and testing/calibration laboratories to measure their optical and electrical properties with high accuracy. Measuring HP-LEDs has been difficult because they are highly sensitive to their junction temperatures, which rise rapidly when they are turned on. Various methods have been proposed and used to measure HP-LEDs, but most of them are only useful for particular applications and unable to produce accurate and reproducible measurement results. To address the measurement need, the Illuminating Engineering Society (IES) recently approved three methods that can be used for the measurement of HP-LEDs, which are the DC method, single-pulse method, and continuous-pulse method [1]. All three measurement methods refer to the junction temperature of an HP-LED as the thermal condition and thus, the measured results are considered to be equivalent as long as the junction temperature is set to be the same. However, our recent study shows that the difference in the measurement results of the three different methods can be significant (e.g., 5 % in total luminous flux) due to significant heating of the junction and/or phosphor material of the HP-LED during the period of a measurement. In this paper, we will describe the measurement of HP-LEDs using the three different methods, compare the measurement results, and discuss the cause that results in the significant difference. [1] Illuminating Engineering Society, “IES LM-85-14: Approved Method: Electrical and Photometric Measurements of High-Power LEDs.” (2014)