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Pure Appl. Chem., 2006, Vol. 78, No. 6, pp. 1239-1252

Metal halide lamps: Gravitational influence on color separation

W. W. Stoffels1, A. J. Flikweert1, T. Nimalasuriya1, J. J. A. M. van der Mullen1, G. M. W. Kroesen1 and M. Haverlag2

1 Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
2 Central Development Lighting, Philips Lighting, P.O. Box 80020, 5600 JM Eindhoven, The Netherlands

Metal halide lamps are very efficient light sources based on a Hg plasma arc with metal halide salt additions. In spite of their high efficiency, the lamps suffer from several problems, such as color separation and instabilities, which currently hinder large-scale use. These phenomena are caused by a complex interaction of convection and diffusion flows in the plasma. In order to unravel the various contributions, experiments under microgravity have been performed where convection is absent.
The experiments confirm the previously held qualitative views, but also provide absolute data on densities and temperatures that will be used to validate numerical models of these lamps.