A lamp unit for a motor-vehicle headlamp, comprising: at least one dipped-beam module for generating a dipped-beam light distribution, for the most part below a horizontal cut-off line imaged substantially in front of the motor vehicle, at least one main-beam module for generating a main-beam light distribution, for the most part above the cut-off line, an imaging optical element (103, 503) connected downstream of the dipped-beam module and the main-beam module in the optical beam direction for generating a total light distribution of the light modules, having an optical axis (104, 204, 404, 504) and a focal surface orientated substantially normal to the optical axis (104, 204, 404, 504), and a diaphragm (105, 405), which has a diaphragm edge (106, 206, 306, 506) and extends essentially up to the focal surface of the imaging optical element (103, 503) for generating the horizontal cut-off line in a light image generated by the lamp unit, characterized in that the diaphragm (105, 405) has a substantially flat opaque diaphragm region (107, 407) and has a transparent diaphragm region (108, 408) with a geometric structure (109, 409) made from a transparent material at the diaphragm edge (106, 206, 306, 506) in the region of the focal surface, wherein the geometric structure (109, 409) comprises at least one prism body (110, 210, 310, 410, 510) with a substantially triangular cross-sectional area, the at least one prism body (110, 210, 310, 410, 510) is elongated and the longitudinal extent runs substantially transversely to the optical axis (104, 204, 404, 504), the at least one prism body (110, 210, 310, 410, 510) has a first, a second and a third prism surface, wherein the first prism surface (111, 211, 311, 511) is substantially flush with the flat opaque diaphragm region (107, 407), the second prism surface (112, 212, 312, 512) faces the opaque diaphragm region (107, 407) and encloses an internal angle α1 ≥ θ with the first prism surface (111, 211, 311), and the third prism surface (113, 213, 313, 513) faces away from the opaque diaphragm region (107, 407) and encloses an internal angle a2 ≥ θ with the first prism surface (111, 211, 311), wherein θ is the critical angle of total internal reflection of the transparent material, the internal angles a1 and a2 are the same or different, and with the proviso that the internal angle a1 or the internal angle a2 is not 45°. at least one dipped-beam module for generating a dipped-beam light distribution, for the most part below a horizontal cut-off line imaged substantially in front of the motor vehicle, at least one main-beam module for generating a main-beam light distribution, for the most part above the cut-off line, an imaging optical element (103, 503) connected downstream of the dipped-beam module and the main-beam module in the optical beam direction for generating a total light distribution of the light modules, having an optical axis (104, 204, 404, 504) and a focal surface orientated substantially normal to the optical axis (104, 204, 404, 504), and a diaphragm (105, 405), which has a diaphragm edge (106, 206, 306, 506) and extends essentially up to the focal surface of the imaging optical element (103, 503) for generating the horizontal cut-off line in a light image generated by the lamp unit, characterized in that the diaphragm (105, 405) has a substantially flat opaque diaphragm region (107, 407) and has a transparent diaphragm region (108, 408) with a geometric structure (109, 409) made from a transparent material at the diaphragm edge (106, 206, 306, 506) in the region of the focal surface, wherein the geometric structure (109, 409) comprises at least one prism body (110, 210, 310, 410, 510) with a substantially triangular cross-sectional area, the at least one prism body (110, 210, 310, 410, 510) is elongated and the longitudinal extent runs substantially transversely to the optical axis (104, 204, 404, 504), the at least one prism body (110, 210, 310, 410, 510) has a first, a second and a third prism surface, wherein the first prism surface (111, 211, 311, 511) is substantially flush with the flat opaque diaphragm region (107, 407), the second prism surface (112, 212, 312, 512) faces the opaque diaphragm region (107, 407) and encloses an internal angle α1 ≥ θ with the first prism surface (111, 211, 311), and the third prism surface (113, 213, 313, 513) faces away from the opaque diaphragm region (107, 407) and encloses an internal angle a2 ≥ θ with the first prism surface (111, 211, 311), wherein θ is the critical angle of total internal reflection of the transparent material, the internal angles a1 and a2 are the same or different, and with the proviso that the internal angle a1 or the internal angle a2 is not 45°.