Arc tube having reduced length, low-pressure mercury lamp, and lighting apparatus

摘要

A low-pressure mercury lamp has: an arc tube formed by an arc-tube body in helical configuration, and electrodes provided at respective ends of the arc-tube body; and bases supplying power to the electrodes. The arc-tube body is made of a glass tube winding around an axis A while moving into a direction of the axis A. Ends of the glass tube are positioned away from each other with the winding part therebetween in the direction of the axis A. An outer diameter of the winding part seen in the direction of the axis A is within a range of 16 mm to 38 mm.