Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Deviations From Equilibrium of Thallium Level Populations in a Metal Halide Arc Lamp



D Karahourniotis, John J. Curry, E Drakakis, Eric C. Benck


The excitation equilibrium in a metal halide lamp was studied using a method based on optically thick lines without the assumption of local thermodynamic equilibrium (LTE). The lamp has a diameter of 15.4 mm, an electrode gap of 28 mm, and was operated with an electromagnetic ballast at 60 Hz and 265 W. The lamp contains 16 mg of Hg, 0.3 mg of TlI, 0.4 mg of TmI3, and 0.5 mg Ar. The working pressure is approximately 3 atm. A 3.3 m Czerny-Turner spectrograph in combination with an intensified charge-coupled device camera were used to obtain time-resolved spectra of self-reversed lines of Tl and Hg. The Tl 5350 and 3776 lines were strongly self-reversed at all times and were studied to determine if they might be used for determination of the electron temperature in much the same way that the Hg 5461 and 4047 lines are used. The Tl lines terminate in the 6 2P1/2 ground level and the 6 2P3/2 metastable level, respectively. These levels are separated by only 0.97 eV and should be strongly coupled by inelastic electron collisions. Analysis of the Tl 5350 and 3776 lines indicates strong deviations from equilibrium in the populations of the Tl 6 2P1/2 and 6 2P3/2 levels. At the time of current zero-crossing, the population of the 6 2P3/2 metastable level is seen to exceed the population of the ground level.
Proceedings Title
Light Sources 2004
Conference Dates
July 18-22, 2004
Conference Location
Toulouse, 1, FR
Conference Title
International Symposium on the Science and Technology of Light Sources


arc lamp, mercury, metal-halide, plasma, spectroscopy, thallium


Karahourniotis, D. , Curry, J. , Drakakis, E. and Benck, E. (2004), Deviations From Equilibrium of Thallium Level Populations in a Metal Halide Arc Lamp, Light Sources 2004, Toulouse, 1, FR (Accessed May 20, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created June 30, 2004, Updated October 12, 2021