Modelling mercury-free HID lamps: Breakdown characteristics and thermodynamics

The modelling of mercury free HID lamps is challenging due to the complexity of gas mixtures and sensitivity of breakdown characteristics to the initial physical conditions. In this paper we report on results from a computational investigation of breakdown characteristics and the plasma properties of mercury-free HID lamps having metal halide fills. We discuss breakdown time as a function of voltage rise times, polarities and plasma composition (e.g., hot and cold restart). We also discuss the thermodynamic properties for doses containing Xe/NaI/ScI3/ZnI2.. The simulator used in this work, nonPDPSIM, is a plasma hydrodynamics model in which continuity, momentum and energy equations are solved for charged species with solution of Poisson's equation. The model is coupled with a thermodynamics module providing local thermodynamic equilibrium (LTE) properties. Algorithms were developed to represent the transition of the lamp from a kinetics-Poisson regime during breakdown to an LTE-ambipolar regime as the arc begins to form. BREAKDOWN CHARACTERISTICS The breakdown process of HID lamps can b