Clear T17 mercury lamp - run up

The lamp shown here is an experimental 52 m-wide low-pressure argon-mercury discharge lamp (a sort of T17 fluorescent tube without coating) built with high-current (0.9 A) SOX beehive electrodes. The sequence here shows the discharge run up, first starting in an atmosphere dominated by the argon buffer (top), and then reaching steady-state regime with enough mercury in the gas phase to dominate the plasma's radiative processes (bottom). This lamp was made to study the properties of high-current low-pressure discharges of the kind found in induction lamps such as the Philips QL. To reproduce operating conditions, the argon fill pressure is much lower (less than a millibar) than in standard fluorescent tubes (4 millibars, typically). Electrodes are used here to couple a current to the discharge because this results in a plasma geometry that is easier to study than in inductively-coupled lamps (i.e. a cylinder shape instead of a toroid).