DISCHARGE LAMP, DISCHARGE LAMP LIGHTING METHOD, DISCHARGE LAMP LIGHTING DEVICE, AND LIGHTING SYSTEM

PROBLEM TO BE SOLVED: To increase the amount of light in the longitudinal direction of a discharge container, and to provide uniform light distribution, and improve cost performance with easy insulation. SOLUTION: A rare gas is enclosed in a slender discharge container 1, and a pair of internal electrodes 2 are sealed at both ends of the discharge container 1, further an external electrode 3 is longitudinally set on the external surface of the discharge container 1. A lamp current density ID (mA/cm2) obtained by dividing a rated lamp current (mA) by an area(cm2) of the external electrode 3 is set in the range of the following formula in relation to an enclosing pressure P(Torr) of the rare gas, -0.002×P+3.0816>ID>0.001×P-0.0151. The width of the longitudinal central portion of the external electrode 3 is set wider than that of both ends of it, thereby light distribution can be more evened relatively. Annular conductors are arranged in the positions opposite to the internal electrodes 2 of the discharge container 1 and they are connected to the external electrode 3, which eliminates the flicker of brightness generated in the vicinity of the internal electrodes 2.