Discharge bulb and automobile headlamp

摘要

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.