Signal lamp for a motor vehicle with a complex reflector design is presented. The reflector is composed of set of rectangular bicubic Bezier ‘pillows’ creating desired horizontal and/or vertical light spread. Cover lens with no or weakly-spreading optics is assumed. Mathematical background is discussed in part 2 - parametric equations for individual pillow are presented, equations for control points ensuring proper optical function of the pillow are derived and parameter controlling intensity distribution of output beam is introduced. Option to prevent beam asymmetry of conventional signal lamps with big rake angles of cover lens using ‘semicomplex’ optical system (i.e. complex reflector combined with optical elements on the cover lens) is discussed, too.