High pressure discharge lamp and method for sealing a bulb thereof

A method for sealing a bulb of a high pressure discharge lamp including a first electrode and a second electrode, said first and second electrodes being disposed in said bulb having a first insertion opening and a second insertion opening so as to be opposite the other, comprising the steps of:

• disposing said first electrode at said first insertion opening so that said first electrode is placed at a predetermined position in the axial direction;
• heating a predetermined portion of said first insertion opening while maintaining a pressure difference between the inside and outside of said bulb;
• shrinking said predetermined portion of said first insertion opening in a natural state so that a part of said first electrode is sealed with said predetermined portion;
• disposing said second electrode at said second insertion opening so that said second electrode is placed at a predetermined position in the axial direction;
• heating a predetermined portion of said second insertion opening while maintaining a pressure difference between the inside and outside of said bulb;
• and
• shrinking said predetermined portion of said second insertion opening in a natural state so that a part of said second electrode is sealed with said predetermined portion, wherein
• the length of a contacting portion formed by sealing said part of said first electrode with said bulb, and by said part of said second electrode with said bulb, is in the range between:
• a maximum length, Lmax, defined as:
• Lmax(mm)≦200/(P×D);
• and
• a minimum length, Lmin, defined as:
• Lmin(mm)≧08/(D2×π)or Lmin(mm)≧0.7 whichever is longer,
• where D is the diameter (mm) of said first electrode or said second electrode and P is the power (W) supplied to said first electrode or said second electrode.

A high pressure discharge lamp, comprising:

• a quartz glass bulb;
• conductive elements, said conductive elements being airtightly sealed at sealing portions of said quartz glass bulb;
• and
• a pair of electrodes, each electrode of said pair of electrodes being disposed so as to be opposite the other and each of said electrodes being connected to one of said conductive elements, wherein
• Rmax of an end portion of each of said electrodes is about 5 μm or less,
• where Rmax is the maximum of the absolute value of the difference between the distance from the axial center of each of said electrodes to a particular point on the surface of each of said electrodes and the mean value of the distance.