Issues of thermal testing of AC LEDs

In this paper we aim at highlighting different aspects of thermal testing of AC LEDs, especially of retrofit LED lamps which are directly driven from the AC mains supply. The main focus is the concept of thermal impedance applied for AC driven LEDs and the AC heating power. The paper gives an overview of the different representations of the thermal impedance then provides estimates of the AC power of LEDs for one of the extreme cases (ideal AC voltage generator driven situation) together with spectra of harmonics of the AC heating power. Definitions and test procedures for the AC thermal impedance of LEDs are suggested along with test environments for AC LED modules as well as for complete retrofit LED lamps.