LOW-PRESSURE MERCURY VAPOR DISCHARGE LAMP AND COMPACT FLUORESCENT LAMP

摘要

A low-pressure mercury vapor discharge lamp is provided with a discharge vessel (10). The discharge vessel (10) encloses a discharge space (11) provided with a filling of mercury and a rare gas in a gastight manner. According to the invention, the discharge vessel is made from a glass comprising silicon oxide and sodium oxide in the following percentages by weight: SiO2 60 - 80 wt.% and Na2O 10 - 20 wt.%. Preferably, the glass composition comprises SiO2 70-75 wt.%, Na2O 15-18 wt.% and K2O 0.25-2 wt.%, so that this glass is a so-called sodium-rich glass as compared to the customarily used mixed alkali glass. At least a part of an inner surface of the discharge vessel (10) is provided with a transparent layer (16) comprising 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. Preferably, the transparent layer (16) comprises yttrium borate and strontium borate. Preferably, the transparent layer (16) has a thickness between 5 nm and 200 nm. A luminescent layer (17) is preferably provided on top of the transparent layer in the discharge vessel. The discharge lamp according to the invention has a comparatively high maintenance.