Lighting device for vehicle

The device e.g. luminous headlight (1), has a case fixed to a chassis of a motor vehicle via an assembling interface comprising retaining brackets (20). An optical module is mounted on the case via another assembling interface comprising fixation points (25), and emits a light beam directed towards an opening of the case. A flat stiffening plate (40) limits thermal expansion of one of the interfaces. The case has a heat sink that dissipates heat towards an exterior of the case. The case has a set of stiffening ribs arranged at the proximity of the interface.