Abstract: By applying radiation beam energy to a contact portion between an end portion 7 of a glass tube 1 and a zinc-mercury alloy drop 6 and the vicinity thereof by means of an optical fiber 5, the alloy drop 6 is directly heated so as to be caused to partly melt at a bottom portion thereof and fixed firmly to an inner wall surface of the end portion 7 of the glass tube without causing variations.

Abstract: Two arc tubes which are to be connected are held at different levels. Predetermined portions in the vicinity of an end of each arc tube are evenly heated and softened by a flame of a burner from the side. An air flow is supplied to blowing up the softened portion to form a semi-junction bridge having a circular cross-section and a flat connecting face. The thickness of the wall of the semi-junction bridge is even. The arc tubes having the semi-junction bridges are disposed on the same plane and one arc tube is moved to the other to connect the semi-junction bridges while the connecting faces are softened.

Abstract: This invention provides a compact, efficient and well-designed circular fluorescent lamp with high output power. The circular fluorescent lamp has less non-luminant region and good characteristics of luminous intensity distribution, and keeps high level of lamp lumen output. Circular arc tubes are disposed concentrically on the same plane. Electrodes are attached to the tube-end parts of the one side of the circular arc tubes respectively, and the other tube-end parts of non-electrode side are sealed. The circular arc tubes are joined each other near the tube-end parts of the non-electrode side with a bridge-jointed portion, so that a discharge path is formed between the electrodes inside the arc tubes. The tube outer diameter of the circular arc tubes is 14 mm, the circle outer diameter of the outer circular arc tube is 150 mm, and the circle inner diameter of the inner arc tube is 90 mm.