Abstract: There is provided a novel method of lighting an ultra-high pressure discharge lamp (A1) having a discharge bulb (1) made of quartz glass in which a pair of electrodes (2) and (3) are disposed facing each other, the method including: lighting the lamp with alternating current; and providing a time period of at least one second for which the alternating current assumes a lighting frequency of 5 Hz or lower during a period for which the lamp lights, wherein the electrodes (2) and (3) each have a current withstanding capability against a current 1.5 times or more as high as a current value at which the lamp lights stably. This method enables the ultra-high pressure discharge lamp to have a longer life and exhibit a higher luminance.

Abstract: There is provided a novel method of lighting an ultra-high pressure discharge lamp (A1) having a discharge bulb (1) made of quartz glass in which a pair of electrodes (2) and (3) are disposed facing each other, the method including: lighting the lamp with alternating current; and providing a time period of at least one second for which the alternating current assumes a lighting frequency of 5 Hz or lower during a period for which the lamp lights, wherein the electrodes (2) and (3) each have a current withstanding capability against a current 1.5 times or more as high as a current value at which the lamp lights stably. This method enables the ultra-high pressure discharge lamp to have a longer life and exhibit a higher luminance.

Abstract: A metal halide lamp includes a pair of electrodes with a spacing of 0.5 to 1.5 mm therebetween, an envelope enclosing the pair of electrodes, and at least one metal halide, other than a mercury halide, that is encapsulated in the envelope in an amount of from 0.04 to 0.3 mg/cc, wherein the metal halide lamp operates in a power range from 75 to 270 watts per millimeter across the spacing between the pair of electrodes.