The present invention relates to an improved maintenance, low-pressure mercury vapor discharge lamp having a discharge vessel enclosing a discharge space provided with a filling of mercury and a rare gas in a gastight manner. The discharge vessel is made from a glass of essentially 60-80% by weight SiO.sub.2 and 10-20% by weight Na.sub.2 O. Preferably, the composition of this so-called sodium-rich glass is made of 70-75% by weight SiO.sub.2, 15-18% by weight Na.sub.2 O and 0.25-2% by weight K.sub.2 O. At least a part of the inner surface of the discharge vessel is provided with a transparent layer having a borate or a phosphate of an alkaline-earth metal and/or of scandium, yttrium or another rare earth metal. Preferably, the alkaline-earth metal is calcium, strontium and/or barium. In a particularly preferred embodiment, the transparent layer is made of yttrium borate and strontium borate. Additionally, the transparent layer preferably has a thickness between 5 and 200 nm and has provided on it a luminescent layer.