Atomic and Excitation Temperatures in Medium- and High-pressure Mercury Arc Lamps

Atomic and excitation temperatures were determined in medium-pressure (0.14 atm) mercury lamp working on square-wave current from radiance measurements of the red wing of the resonance mercury line 254 nm. The results were compared with these obtained using time resolved measurements at the maximum- and minimum current phase in a high-pressure (6 atm) mercury lamp operating with typical conventional electromagnetic ballast, and show that strong nonequilibrium phenomena occur in particular in the medium-pressure lamp. The excitation temperature was determined from the peak radiance using a non-LTE version of the Bartels method. The atomic temperature as well as the plasma pressure was then deduced from a non-LTE simulation of the line shape.