The present invention provides a high pressure discharge lamp which is provided
with a discharge tube containing a pair of electrodes therein and being filled
with mercury, an inert gas and a halogen gas, the amount of the mercury filled
being 0.12 to 0.35 mg/mm3, the halogen gas being at least one gas selected
from the group consisting of Cl, Br and I and being present in an amount of 10-7
to 10-2 mol/mm3, and the electrodes being mainly
composed of tungsten, and the tungsten as a material of the electrodes contains
not more than 12 ppm of potassium oxide (K2O). In such a high pressure
discharge lamp, blackening of the discharge tube due to the potassium oxide (K2O)
contained in the tungsten, and decrease in illumination maintenance can be prevented,
thus providing a high pressure discharge lamp with a long lifetime, a lighting
optical apparatus using the high pressure discharge lamp as a light source, and
an image display system using the lighting optical apparatus. In another aspect,
the amount of —OH in the glass of the discharge tube is less than 3 ppm.
In a further aspect, the discharge lamp has a restriking voltage of less than 20 V.
