The invention refers to a Lighting system comprising: a LED board bearing LEDs; and an optical board on the LED board; wherein the optical board is made of optical modules positioned side-by-side according to predetermined orientations one to the other, each optical module comprising at least one optical element adapted to face at least one of said LEDs and modify feature of the light emitted by this at least one LED, wherein the lighting system is provided with mechanical fool proofing elements adapted to prevent a positioning of the optical modules according to orientations one to the other different from said predetermined orientations.