An interchangeable headlamp reflector and light bulb unit is provided which can be used as part of various automotive headlamp assemblies. The surface of the reflector is defined mathematically by considering the optical path differences between a ray of light from a light source and a ray of light from a vertical cylindrical axis. The reflector is made of a low number of individual segments that each define a certain portion of the resulting beam of light. Each segment has light rays that extend parallel to the ground and diverge horizontally, thus minimizing possible hot spots on the lens of the reflector assembly.