An investigation into the replacement of mercury by indium iodide or tin halides in high-intensity discharge lamps

  • T.L. Lemmens

Student thesis: Master


In this study we investigated the possibility to replace mercury by metalhalide molecules in the filling of CMH lamps, since mercury is a poisonous substance. Indium iodide was considered a viable alternative, because atomic indium has a high electron-atom collisional cross section.Several lamps were created, in which the indium iodide content was varied, as well as the addition of sodium iodide and dysprosium iodide. The spectra of the lamps were measured in an integrating sphere and their energy balances were determined. The spectra showed that indium iodide emits a broad continuum in the visible and infrared part of the spectrum. There was also a complete absence of ultraviolet radiation. The plasma propertiesin the core of the discharge were determined from the integrating-sphere measurements. Atomic indium lines were used to calculate the core temperature, and a simplified model, developed by Elenbaas, was used to calculate the atomic indium and electron densities. This way, we determined that the broad band continuum was not caused by bremsstrahlung or recombination radiation, but rather by molecular radiation emitted by InI molecules.Varying the indium iodide content in the lamps confirmed that indium iodide increased the resistivity of the lamps and indeed functioned as a buffer gas. However, the application of the Elenbaas model on the integratingsphere measurements suggested that indium iodide led to contraction of the arc column. A seperate side-on setup was created to measure the spectrum as a function of the lateral position in the lamp. A series of measurements over the total lateral width of the lamp were Abel transformed in order to create a radial temperature profile, which showed contraction of the arc. This was also confirmed by photos taken with a cross polarized filter. Contraction by indium iodide can lead to arc instability and limits the use of additives in CMH lamps.A different set of lamps was created that contained tin bromide and tin iodide as an alternative to mercury. These were only measured in the integrating sphere. The spectra of these lamps showed the same trends as the indium iodide lamps. We therefore concluded that neither indium iodide nor tin halides are a suitable alternative to mercury.
Date of Award31 Aug 2013
Original languageEnglish
SupervisorA.J. Rijke (Supervisor 1), Sander Nijdam (Supervisor 2) & Gerrit M.W. Kroesen (Supervisor 2)

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