been investigated . However, the thermal resistance obtained from DC mode cannot be directly applied to AC mode measurements due to the variable input power in AC. The thermal characteristics of LED under AC source had never been investigated so far to the best knowledge of the authors. In this paper, we report on both experimental and analytical thermal analysis of AC driven LED packages. A comparison was made between the DC driven and the AC driven thermal performance and between the simulated and the experimental results for the AC driven LEDs.