Abstract: A fluorescent lamp of high brightness and compact size is provided by constructing the envelope from two or more phosphor-coated open-ended glass tubes that are held in bundled columnar relationship by a dome-shaped cap which is also phosphor coated and defines an end chamber that is common to each of the tubes. The opposite ends of the tubes are closed and contain electrodes so that one or several arc discharges can pass between the electrodes by traversing the interconnecting end chamber and the associated tubes when the lamp is energized. If three or more arc tubes are used, operation of the lamp in either a single or multiple-discharge mode can be achieved by selectively energizing different pairs of electrodes and tubes. Operating circuits for energizing a three-tube lamp and a four-tube lamp in such a manner are disclosed.