A light source device including a light-guiding pillar, an opaque layer,
and a light source is provided. The light-guiding pillar has a light
incident surface and a light emitting surface, and the light incident
surface is adjacent to the light emitting surface. In addition, the
opaque layer is disposed on the surfaces of the light-guiding pillar
outside the light incident surface and the light emitting surface. The
light source is disposed near the light incident surface. The light
emitted from the light source propagates into the light-guiding pillar
through the light incident surface, and then emits from the light
emitting surface.