Abstract: Arc discharged by a short arc discharge lamp can be made so small in diameter as to appear like a spot. Therefore, the illuminance efficiency of the short arc discharge lamp can be made high and its brightness can also be enhanced.

Abstract: In order to maintain an ultraviolet-ray intensity of a metal halide lamp for a long period, the present invention provides a high intensity discharge lamp comprising an arc tube having electrodes at its both ends, and a rare gas, mercury, iron, a halogen and silver enclosed in the tube, wherein a gram atom ratio of silver to iron is 0.05 to 0.2. The present invention also provides a high intensity discharge lamp comprising an arc tube having electrodes at its both ends, and a rare gas, mecury, iron, a halogen, tin and silver enclosed in the tube, wherein ([Fe]+[Sn])/[J]<0.5 and (2[Fe]+2[Sn]+[Ag])/[J]>1, where [Fe], [Sn], ]Ag] and [J] are, respectively, gram atoms of iron, tin, silver and the halogen.

Abstract: A pulse generating apparatus includes a base current supply section for generating a constant DC current having a first prescribed current level for turning on a xenon lamp, and a pulse current section for adding a pulse current having a second current level greater than the first current level and a prescribed pulse duration within a prescribed repetition period to the constant DC current. The base current supply section and pulse current section should satisfy the following equations:1.4.ltoreq.Imax/Imini.ltoreq.60.2.ltoreq.t/T.ltoreq.0.7T.ltoreq.1/40Where Imax is the sum of the first and the second prescribed current levels, Imini is the first prescribed current level, T is the prescribed repetition period, and t is the prescribed pulse duration.When the pulse current added to the DC current is supplied to a xenon lamp, the xenon lamp outputs a strong light during the pulse duration of the pulse current, and a feeble light during the absence of the pulse current.