Patent ID: 7075232

Claim:
A high pressure discharge lamp having a pair of electrodes formed of tungsten opposed in a discharge vessel of an arc tube in which mercury, a bromide and a rare gas are sealed, each of the top ends of the electrodes is formed into a substantially semispherical shape, and a protrusion to form an arc spot by the discharge between the electrodes is formed at the top end thereof, wherein the conditions of the following formulae 1 to 3 are satisfied when assuming, an inter-electrode distance between both of the electrodes as L(mm), a lamp current during stable lighting as I(A), a molar amount of bromine in the bromide sealed in the discharge vessel of the arc tube as X(mol), an inner volume of the discharge vessel of the arc tube as Y(ml), and a weight of tungsten at the top end of each electrode formed into a substantially semispherical shape as W(mg): 0.3 â‰¦L/Iâ‰¦ 1.0â€ƒâ€ƒFormula 1: 1.2Ã—10 âˆ’7 â‰¦X/Yâ‰¦ 1.1Ã—10 âˆ’5 Formula 2: 9 â‰¦W 3/2 /Iâ‰¦ 65â€ƒâ€ƒFormula 3.