Low-pressure mercury vapor discharge lamp, particularly U-shaped fluorescent lamp, and method of its manufacture

A low-pressure mercury vapor discharge lamp having a discharge envelope (1;

• 15) formed of a single-piece glass tube bent at least once to define at least two straight, parallel longitudinal tube sections (2, 3;
• 16, 17, 18, 19) of essentially identical diameter dimensions (DL) and at least one transverse tube section (4;
• 20, 21, 22) connecting individual longitudinal tube sections;
• a fluorescent coating on said longitudinal tube sections and on at least one transverse tube section;
• the two outer ends of the discharge envelope being sealed and including electrodes sealed therein;
• and a mercury-containing gas fill in said envelope,
• wherein, in accordance with the invention,
• the envelope is shaped and arranged to provide, in operation of the lamp, cold spots controlling the operating pressure of the fill in the envelope,
• said envelope being formed and shaped to define an outer generating line M.sub.Q of the individual transverse tube sections (4;
• 20, 21, 22) which is substantially straight;
• a diameter D.sub.LQ in the tube bends (5, 6;
• 23, 24, 25, 26, 27, 28) at the transition between the longitudinal tube sections (2, 3;
• 16, 17, 18, 19) and the respective transverse tube section (4;
• 20, 21, 22) which is larger than the diameter D.sub.Q of the individual transverse tube section in the middle thereof,
• and a diameter D.sub.Q of the transverse tube section which is at least as large as the diameter D.sub.L of the longitudinal tube sections.