Discharge tube having a double-tube type structure

A light source for emitting light in a desired direction, comprising:

• a discharge tube which includes:
• an inner bulb including a bulb wall having an inner surface for defining an arc discharge chamber for enclosing therein gas for emitting light and an outer surface for defining an outer diameter of a first value and a pair of solid portions continuously connected from the bulb wall, each for supporting a corresponding one of a pair of electrodes and a corresponding one of a pair of metal members which is connected to the corresponding one of the pair of electrodes, the pair of electrodes being projected in the arc discharge chamber from the pair of solid portions and the pair of metal members being projected outwardly of the inner bulb from the pair of solid portions, the pair of solid portions having an outer surface;
• and an outer tube for sealingly enclosing therein the inner bulb, the outer tube including a tube wall having a large-diameter part having an inner surface for defining a large-diameter hollow portion and a small-diameter cylindrically-shaped part continuously connected from the large-diameter part, the small-diameter cylindrically-shaped part having an inner surface for defining a small-diameter hollow portion and an outer surface defining a substantially constant outer diameter of a second value which is equal to or smaller than the first value, said inner bulb being enclosed in said outer tube with the metal members projected outwardly of said inner bulb being supported by said tube wall, the large-diameter hollow portion receiving therein an entire part of the arc discharge chamber of said inner bulb with a gap being formed between the outer surface of the bulb wall of said inner bulb and the inner surface of the large-diameter part of said outer tube, the small-diameter hollow portion receiving therein at least a part of one of the pair of solid portions of said inner bulb and the metal member projected from the solid portion with a gap being formed between the outer surface of the part of the solid portion of said inner bulb and the inner surface of the small-diameter cylindrically-shaped part of said outer tube;
• and
• a reflective mirror for receiving the light emitted from the arc discharge chamber and reflecting the light in a desired direction, said reflective mirror being formed with a support wall having an inner surface extending along a predetermined axis and defining a through-hole for receiving therein the small-diameter cylindrically-shaped part of the outer tube of said discharge tube.

A discharge tube for emitting light, comprising:

• an inner bulb including a bulb wall having an inner surface for defining an arc discharge chamber for enclosing therein gas to emit light and an outer surface and a pair of solid portions continuously connected from the bulb wall, each for supporting a corresponding one of a pair of electrodes and a corresponding one of a pair of metal members which is connected to the corresponding one of the pair of electrodes, the pair of solid portions having an outer surface, the pair of solid portions extending along a predetermined axis from a pair of positions of the bulb wall defining opposite sides of the arc discharge chamber along the predetermined axis, the bulb wall having a cross section along a plane perpendicular to the predetermined axis which has a second outer size defined by the outer surface of the bulb wall, the first outer size varying along the predetermined axis and having a first value at a maximum, the pair of electrodes being projected inside of the arc discharge chamber from the corresponding solid portions along the predetermined axis and the pair of metal members being projected outwardly of said inner bulb from the corresponding solid portions along the predetermined axis;
• and
• an outer tube for sealingly enclosing therein said inner bulb, said outer tube including a tube wall having a large-size part having an inner surface for defining a large-size hollow portion and a pair of small-size parts extending along the predetermined axis from opposite sides of the large-size part along the predetermined axis, the pair of small-size parts having a pair of outer surfaces and a pair of inner surfaces for defining a pair of small-size hollow portions, each of the pair of small-size parts having a cross section along a plane perpendicular to the predetermined axis which has a second outer size defined by the outer surface of the corresponding small-size part, the second outer size being substantially constant along the predetermined axis and having a second value which is equal to or smaller than the first value, said outer tube enclosing therein said inner bulb in such manner that the large-size hollow portion receives therein an entire part of the bulb wall of said inner bulb, with a gap being formed between the outer surface of the bulb wall and the inner surface of the large-size part, and each of the pair of small-size hollow portions receives therein at least a part of a corresponding one of the pair of solid portions of said inner bulb and a corresponding one of the pair of metal members projected from the corresponding one of the pair of solid portions, with a gap being formed between the outer surface of the corresponding solid portion and the inner surface of the corresponding small-size hollow portion.

A light source for emitting light in a desired direction, comprising:

• a discharge tube which includes:
• an inner bulb including a bulb wall having an outer surface and an inner surface for defining an arc discharge chamber for enclosing therein gas to emit light and a pair of solid portions continuously connected from the bulb wall, each for supporting a corresponding one of a pair of electrodes and a corresponding one of a pair of metal members which is connected to the corresponding one of the pair of electrodes, the pair of solid portions having an outer surface, the pair of solid portions extending along a predetermined axis from a pair of positions of the bulb wall defining opposite sides of the arc discharge chamber along the predetermined axis, the bulb wall having a cross section along a plane perpendicular to the predetermined axis which has a first outer size defined by the outer surface of the bulb wall, the first outer size varying along the predetermined axis and having a first value at a maximum, the pair of electrodes being projected inside of the arc discharge chamber from the corresponding solid portions along the predetermined axis and the pair of metal members being projected outwardly of said inner bulb from the corresponding solid portions along the predetermined axis;
• and
• an outer tube for sealingly enclosing therein said inner bulb, said outer tube including a tube wall having a large-size part having an inner surface for defining a large-size hollow portion and a pair of small-size parts extending along the predetermined axis from opposite sides of the large-size part along the predetermined axis, the pair of small-size parts having a pair of outer surfaces and a pair of inner surfaces for defining a pair of small-size hollow portions, each of the pair of small-size parts having a cross section along a plane perpendicular to the predetermined axis which has a second outer size defined by the outer surface of the corresponding small-size part, the second outer size being substantially constant along the predetermined axis and having a second value which is equal to or smaller than the first value, said outer tube enclosing therein said inner bulb in such a manner that the large-size hollow portion receives therein an entire part of the bulb wall of said inner bulb, with a gap being formed between the outer surface of the bulb wall and the inner surface of the large-size part, and each of the pair of small-size hollow portions receives therein at least a part of a corresponding one of the pair of solid portions of said inner bulb and a corresponding one of the pair of metal members projected from the corresponding one of the pair of solid portions, with a gap being formed between the outer surface of the corresponding solid portion and the inner surface of the corresponding small-size hollow portion;
• and
• a reflective mirror for receiving light emitted from the arc discharge chamber and for reflecting light in a desired direction, said reflective mirror being formed with a support wall having an inner surface extending along the predetermined axis and defining a through-hole for receiving therein one of the pair of small-size parts of the outer tube of said discharge tube.