Light-emitting device for a motor vehicle headlight and headlight provided with said device

The device (1) has a housing (6), and a light source arranged on the housing. An optical device directs light beams emitted by the light source. The housing comprises a projecting element for allowing a fixed position of the optical device with respect to the housing. The projecting element comprises a hollow rib (18) formed inside an enclosure (8) defined by the housing. The optical device comprises a hollow rib (32) that nests partially with the hollow rib of the housing. The hollow rib of the housing is rectilinear and/or comprises a number of arms.