Helmar Adler

Understanding the high intensity discharge lamp: The need for more data

High intensity discharge (HID) lamps, in particular the metal halide (MH) lamps, comprise a group of light sources with high efficacy and good color rendering. The basic principle behind this lamp type is well known; however, improvements in light output and life of these lamps can only be achieved by studying detailed processes involving advanced diagnostics and modeling, and materials research. After a brief description of the behavior of a metal halide lamp, examples of research areas and diagnostic methods are shown with the emphasis on data needs.

X‐treme Diagnostics for HID Lamps?

X‐ray induced fluorescence has been used to measure elemental number densities of all constituents in a ceramic metal‐halide discharge lamp. High‐energy synchrotron radiation generated at the Sector 1 Insertion Device beam line at the Advanced Photon Source induced K‐shell fluorescence in the high‐pressure arc plasma. High signal‐to‐noise fluorescence spectra of Hg, Dy, Cs and I could be simultaneously obtained. A method for absolute calibration enabled us to map density distributions of all constituents throughout the whole lamp with a spatial resolution of 1 mm3. Elemental ratios show clear evidence of radial de‐mixing of metal additives. A possible explanation for the on‐axis depletion is ambipolar transport of positive ions out of the center of the arc. The highly successful experiments demonstrate the utility of modern x‐ray sources and methods for diagnostics as new tools for improved understanding of high‐pressure arc discharges.