A method for mounting planar lighting modules on a mounting surface may include: providing on opposite sides of the lighting module fixing indentations opening toward the aforesaid sides, superimposing on said opposite sides of the lighting module stiffening bars having lateral lobes extending into said indentations, and fixing to the mounting surface the stiffening bars superimposed on the opposite sides of the lighting module with the opposite sides of the lighting module sandwiched between the stiffening bars and the mounting surface, whereby the stiffening bars urge the lighting module toward the mounting surface.