A lamp module comprising a lamp holder and a lamp is provided. The lamp holder has a structure with a curved arc surface such that the ends of the structure are inwardly converging. Light from the lamp impinging upon the curved arc surface is scattered out to a linear dimension greater than the original length of the lamp. The scattered light is projected onto the light-inlet surface of a light-guiding plate so that light emerges from the light-emitting surface as a planar light source.