A low-pressure mercury vapor discharge lamp is provided with a light-transmitting discharge vessel, enclosing, in a gastight manner, a discharge space provided with a filling of mercury and a rare gas. The discharge vessel comprises means for maintaining a discharge in the discharge space. At least a portion of an inner wall of the discharge vessel is provided with a translucent layer which-according to the invention has a thickness in the range from 1 to 50 .mu.m and comprises an alkaline-earth-borate.