Numerical investigation on the replacement of mercury by indium iodide in high-intensity discharge lamps

Mercury-free high-pressure discharge lamps have been studied by means of a radial-dependent model. Xenon and indium iodide are chosen as start gas and buffer, respectively. Local thermodynamic equilibrium is assumed with a single temperature for all species. The model consists of the coupled description of the balance equation for the plasma temperature with the radiation transport equation. The plasma composition is calculated according to the Guldberg–Waage, Boltzmann and Saha laws. These laws were supplemented by additional equations specifying the total pressure, constant element ratios and quasineutrality. The model takes into account atomic, molecular as well as continuum radiation. The broadening of the optically thick lines is approximated by Stormberg's approach. The predicted spectrum is compared with a measured one and shows good agreement on a qualitative scale. From this comparison it is concluded that the largest part of the continuum radiation is produced by the free–free and free–bound AX transition in InI.