Measurement of barium loss from a fluorescent lamp electrode by laser-induced fluorescence

Abstract

A laser-induced fluorescence method for measuring the loss rate of barium from Ba-Sr-Ca oxide coated electrodes of low-pressure discharge lamps is presented. The oxide coating from the electrode surface is depleted during lamp operation. Using this technique, the Ba loss rate from an electrode, when it is acting both as a cathode and an anode during ac operation, was measured. A significantly larger amount of neutral barium is detected in the vicinity of the electrode when it acts as an anode over when it acts as a cathode. The consumption rate of Ba and hence the life of an oxide coating depends upon the phase of the lamp current, the shape, and the magnitude of the current supplied by the lamp ballast. The consumption rate for the coating increases linearly with the discharge current. A simplified theoretical analysis of the technique for a three-level atomic system irradiated by a pulse laser beam is discussed.