A series of 150 W quartz metal-halide test lamps containing four different chemistries has been studied with optical emission spectroscopy and x-ray absorption imaging. The four chemistries are pure Hg, Hg-HgI 2 , Hg-NaI and Hg-NaI-DyI 3. Core temperatures and comprehensive distributions of Hg vapour densities were measured and combined to obtain comprehensive gas temperature distributions. The concentrations of additives in these specially designed test lamps were found to be much smaller than is typical for a commercial metal-halide lamp. As a consequence, the core temperatures in all lamps are largely characteristic of a pure Hg discharge. The gas temperature distributions have been used to determine power losses resulting from thermal conduction through the Hg vapour. The fraction of total input power dissipated thermally was found to be 0.49 ± 0.01 in pure Hg, similar to published measurements for such lamps. In the Hg-NaI and Hg-NaI-DyI 3 lamps, thermal losses are 0.41 ± 0.01 and 0.42 ± 0.01, respectively. The Hg-HgI 2 lamp has thermal losses of 0.29 ± 0.03.

The diagnostic technique of x-ray absorption imaging of Hg vapour in high-intensity discharge lamps has been extended. X-ray absorption imaging has been used previously to determine the time-averaged absolute Hg density (Curry J J, Sakai M and Lawler J E 1998 J. Appl. Phys. 84 3066). Now, using an intensified charge-coupled device detector and synchrotron radiation, time-resolved measurements have been made. Although no significant time-dependence was seen as a function of the electrical phase for an electronically ballasted lamp, real-time observations were made of the decaying Hg density during the cool-down period. The cold-spot temperature in a 150 W ceramic lamp containing Hg and rare-earth iodides decreased with a time constant of 48.4 s following arc extinction. The primary limitation to the sensitivity of these measurements has been identified, and methods for overcoming this limitation in future work are proposed. Other aspects of the technique are also discussed.