DISCHARGE LAMP AND LIGHTING SYSTEM

PROBLEM TO BE SOLVED: To improve luminous efficiency as much as possible by using luminescent substance, which radiates ultraviolet ray with a wavelength approximated to that of ultraviolet ray radiated by low pressure mercury vapor discharge, instead of substantially using mercury. SOLUTION: One or more type luminescent substance selected out of groups of silicon Si, boron B, calcium Ca and phosphorus P is filled in an inner tube 1, and an outer tube 4 with a pressure reduced atmosphere inside to encircle the inner tube 1 is provided to keep it warm. The luminescent substance is preferably filled therein in the form of halide. If visible light is attempted to be obtained, a fluorescent substance layer 5 is formed on the inner or outer face of the inner tube 1 or on the inner face of the outer face 4. If the fluorescent substance layer 5 is formed on the inner face of the inner tube 1, fluorescent substance hardly affected by halogen is used and, if the fluorescent substance layer 5 is formed on the outer face of the inner tube 1 or on the inner face of the outer tube 4, the inner tube 1 is made ultraviolet-permeable.