The invention is concerned with a low-pressure mercury vapor discharge lamp comprising a light-transmitting discharge vessel, said discharge vessel enclosing, in a gastight manner, a discharge space provided with a filling of mercury, at least a part of a wall of the discharge vessel being provided with a luminescent composition comprising a first UV-A phosphor of general formula (Gd.sub.1-x-y-zY.sub.xLu.sub.y)PO.sub.4:Ce.sub.z, wherein 0.ltoreq.x<1.0, 0.ltoreq.y<1.0, 0