ABSTRACT
To improve the light-technical properties of HID lamps the use of complex mixtures of metal halides (MH) is increasing. To optimise existing HID lamps and to predict properties of future ML lamps, numerical models can be of great use. Results of such a model developed at Philips Lighting were already reported in [I]. This model solves the energy balance for a cylindrical geometry taking into account chemical equilibrium and species transport by diffusion and radiation. An important shortcoming of this model is that natural convection is not included. For metal halide lamps it is known that natural convection is an important driving force behind radial and axial segregation, which has a considerable influence on the light output properties. To investigate the origin and the effect of axial and radial segregation, the natural convection must be included self-consistently. Since natural convection is driven by temperature gradients, the effect of Ohmic dissipation has to be taken into account. For this purpose the plasma simulation package PLASIMO [2], developed at the Eindhoven University of Technology, is used for calculating the energy balance, the flow-field and the radiative transport for a vertically operating HID lamps. The effect of finite electrodes is taken into account.
