Harmonic modeling of high intensity discharge lamps with magnetic ballast has been extensively studied because they are energy-efficient lighting devices commonly used in industrial and public installations, and can be an important source of harmonics. This kind of modeling usually considers the linear saturation curve of the magnetic ballast and represents the arc voltage by a square waveform. However, both assumptions can be far from describing actual lamp behavior, affecting the accuracy of the model. This paper proposes a novel characterization of high intensity discharge lamps considering both the nonlinear behavior of the magnetic ballast and the non-square waveform of the arc voltage. The accuracy of the new model is validated with experimental measurements and compared to that of the traditional models.