Abstract: A direct-current high-voltage discharge bulb includes a ceramic arc tube body having a discharge emission chamber at a middle portion in a longitudinal direction thereof, a light-emitting substance which is sealed inside the discharge emission chamber together with a starting rare gas, and an anode and a cathode which are disposed so as to face each other inside the discharge emission chamber. An inside diameter of the ceramic arc tube body where the discharge emission chamber is defined is made to gradually decrease from the anode side to the cathode side.

Abstract: A vehicle headlamp including a discharge bulb having a ceramic light emitting tube, the light emitting tube having opposed electrodes and being filled with a light emitting substance; and a reflector, which controls a reflection of a light emitted from the light emitting tube. A cross-sectional shape of the light emitting tube is longer in a lateral direction than in a vertical direction.

Abstract: A direct-current high-voltage discharge bulb includes a ceramic arc tube body having a discharge emission chamber at a middle portion in a longitudinal direction thereof, a light-emitting substance which is sealed inside the discharge emission chamber together with a starting rare gas, and an anode and a cathode which are disposed so as to face each other inside the discharge emission chamber. An inside diameter of the ceramic arc tube body where the discharge emission chamber is defined is made to gradually decrease from the anode side to the cathode side.

Abstract: A discharge bulb is equipped with an arc tube main unit including in a ceramic tube a discharge light emitting chamber where electrodes are provided face to face and a luminescent material is filled, with substantially the lower half of the outer peripheral surface of the ceramic tube covered by a light shielding ember. Light to be emitted from the ceramic tube is also emitted from the upper part and directed to the efficient reflecting surface of the reflector thus raising the luminance intensity of the headlamp. In the process of light distribution design of the reflector, the size of the rectangular light source image to be projected (stuck) along the cutoff line is made slimmer (narrower). By perform light distribution design (of the effective reflecting surface) so as to allow the maximum luminance part to approach the cutoff line, the hot zone gets closer to the cutoff line position with improved long distance visibility.

Abstract: A vehicle headlamp including a discharge bulb having a ceramic light emitting tube, the light emitting tube having opposed electrodes and being filled with a light emitting substance; and a reflector, which controls a reflection of a light emitted from the light emitting tube. A cross-sectional shape of the light emitting tube is longer in a lateral direction than in a vertical direction.