1. Technical Field
Apparatuses and devices consistent with the present invention relate to a vehicle headlamp which includes a projection-type light source and, more particularly, to a vehicle headlamp that effectively uses light non-reflected light as overhead light distribution.
2. Related Art
For example, Japanese Patent Application No. JP-A-2003-317513 describes a related art vehicle headlamp. According to a lamp structure of JP-A-2003-317513, the related art vehicle headlamp includes a projection-type light source unit for a high beam. The projection-type light unit includes a projection lens, a light emitting device, and a reflector for reflecting light emitted from the light emitting device such that the light converges to a rear focus of the projection lens. With this lamp structure, light emitted from the light emitting device is reflected twice by a sub-reflecting surface that extends forward from the front edge of the reflector, and an upward sub-reflecting surface that is provided near a rear focus of the projection lens so as to guide the light to the projection lens. Therefore, in addition to the light distribution pattern for the high beam formed by the reflector and the projection lens, the lamp structure provides a light distribution pattern widely diffused outward to the left and right sides.
Further, Japanese Patent Application No. JP-A-2004-241349 describes another related art vehicle headlamp. The related art vehicle headlamp includes a translucent member where the projection lens, a cut-off line forming shade, a light emitting device, and a reflector are integrally formed. In the lamp structure, a subreflector is formed on an outer surface between the reflector and the projection lens, and light reflected from the subreflector is radiated forward from the outer surface of the projection lens. Therefore, in addition to the light distribution pattern for a low beam that has a cut-off line corresponding to the cut-off line forming shade, the lamp structure provides a small light distribution pattern, which mainly illuminates a central region of the light distribution pattern.
However, the added light distribution patterns described in JP-A-2003-317513 and JP-A-2004-241349 have excessively high luminous flux density (i.e., excessive brightness) as the overhead light distribution used for the light distribution pattern for a low beam. Here, the overhead light distribution denotes light distribution that has low luminous flux density and illuminates a part of an upper portion of the cut-off line of light distribution pattern for a low beam in order to improve the visibility of a road sign or a trade sign provided on the front upper side. The intensity of the overhead light distribution is prescribed in a light distribution standard of a lamp. Accordingly, since the light from the added light distribution patterns in JP-A-2003-317513 and JP-A-2004-241349 becomes glare light against an oncoming vehicle, the lamp structures described above have a disadvantage in that they cannot be used as a headlamp for a low beam.