Semi-empirical model for axial segregation in metal-halide lamps

Diffusive and convective processes in the metal-halide lamp cause an unwanted non-uniform distribution of the radiating metal additive (Dy in our case), which results in colour separation. The axial segregation has been described by Fischer (1976 J. Appl. Phys. 47 2954) for infinitely long lamps with a constant axis temperature. However, for our lamps this is not valid. We propose a semi-empirical extended model. The density inhomogeneity gives a measure for the non-uniformity of the Dy density distribution in the lamp. As an example, this parameter is calculated for some measurements obtained by imaging laser absorption spectroscopy