Abstract: The disclosed invention provides a flat-shaped lightning device where all the components of the lighting unit are embedded in a single-mold, one-piece securing unit made out of a solid matrix. The lighting unit comprises a diffusing panel, a light guiding panel, a light source, a diffusing sheet and may also comprise a gasket and one or more circuit board. All of the parts, in particular, frames, plates, gaskets, that usually constitute the securing unit are replaced with a single-piece solid matrix obtained through a single operation. The lighting device is totally watertight, no parts can be loosened. The invention also provides a method for manufacturing the preferred embodiment of the invention.