Electrode has been noted as a large consumer of input watts in a fluorescent lamp. However, as the electrode Potential drop plays an important role in electron emission and ion generation, it is impossible to decrease them to zero. For the purpose of lowering the electrode loss, a discharge tube which has a Common electrode for two discharge columns is produced. The potential drop and the light output in the common electrode are studied with the aid of oscilloscope and photomultiplier. The discharge takes place in a. c. source, and the phase difference between discharges is continuously varied over the range of ± 180°. Both cathode drop and anode drop in the common electrode decrease by several volts throughout the greater part of period in which the directions of current flows in both discharges are contrary to each other. This is probably due to the lowering of ion loss in the common electrode, because of coexistence of cathode drop and anode drop. Also anodic oscillation disappears throughout that period. Finally, three phase operation of lighting by the fluorescent lamp with a common electrode is proposed in the hope to reduce the electrode loss.

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