A light-directing device adapted for directing light emitted by a light source. The light-directing device includes a light-guiding plate and a directing unit that is disposed adjacent to the light-guiding plate such that a portion of the light emitted by the light source into the light-guiding plate is internally reflected by a first inclined surface thereof to exit the light-guiding plate toward an illuminating region, and another portion of the light emitted by the light source passes through the light-guiding plate, enters the directing unit and is internally reflected by a second inclined surface thereof to exit the directing unit toward the illuminating region.