An energy-saving assembly of an elongate low-pressure mercury vapor discharge lamp (1) and at least one elongate extension (2). The low-pressure mercury vapor discharge lamp includes a light-transmitting discharge vessel (10) enclosing, in a gastight manner, a discharge space (15) provided with a filling of mercury and a rare gas mixture. The rare gas mixture includes at least 50% by volume of krypton. The discharge vessel is provided with a luminescent layer (13). Electrodes (4a; 4b) are arranged in the discharge space for maintaining a discharge in the discharge space. The extensions are provided for connection to the low-pressure mercury vapor discharge lamp. The extension includes an inductance (3). The length of the low-pressure mercury vapor discharge lamp together with the length of the extension is adapted to fit a pre-determined mounting distance of tow-pressure mercury vapor discharge lamps.