A lamp unit, comprising at least one light source, a reflector configured to reflect the light emitted from the at least one light source, wherein the reflector elongates along a principal axis, A, and comprises a first opening for an output of the light emitted from the at least one light source, and an engagement element arranged circumferentially around the reflector in a plane perpendicular to the principal axis, A, a lid element arranged on the first opening of the reflector, the lid element comprising a flange arranged at a rim of the reflector at the first opening, a housing at least partially enclosing the reflector in a circumferential direction of the principal axis, A, a fastening element biasedly engaged with the housing, wherein the flange is at least partially arranged between the fastening element and the housing in a direction parallel to the principal axis, A, and wherein the fastening element is configured to bias the flange in a direction parallel to the principal axis, A, and a gasket arranged circumferentially around the reflector in a plane perpendicular to the principal axis, A, wherein the gasket has a step-wise shape in a cross-section of the plane and comprises a first portion extending transverse to the principal axis, A, and being arranged between the flange and the housing in a direction parallel to the principal axis, A, a second portion extending along the principal axis, A, and being arranged between the housing and the flange in a direction perpendicular to the principal axis, A, and a third portion extending transverse to the principal axis, A, and being engaged with the engagement element, wherein the fastening element is configured to clamp the first portion between the flange and the housing in a direction parallel to the principal axis, A, and to clamp the second portion between the housing and the flange in a direction perpendicular to the principal axis, A, and wherein the third portion, via the engagement element, is configured to press the reflector towards the lid element. at least one light source, a reflector configured to reflect the light emitted from the at least one light source, wherein the reflector elongates along a principal axis, A, and comprises a first opening for an output of the light emitted from the at least one light source, and an engagement element arranged circumferentially around the reflector in a plane perpendicular to the principal axis, A, a lid element arranged on the first opening of the reflector, the lid element comprising a flange arranged at a rim of the reflector at the first opening, a housing at least partially enclosing the reflector in a circumferential direction of the principal axis, A, a fastening element biasedly engaged with the housing, wherein the flange is at least partially arranged between the fastening element and the housing in a direction parallel to the principal axis, A, and wherein the fastening element is configured to bias the flange in a direction parallel to the principal axis, A, and a gasket arranged circumferentially around the reflector in a plane perpendicular to the principal axis, A, wherein the gasket has a step-wise shape in a cross-section of the plane and comprises a first portion extending transverse to the principal axis, A, and being arranged between the flange and the housing in a direction parallel to the principal axis, A, a second portion extending along the principal axis, A, and being arranged between the housing and the flange in a direction perpendicular to the principal axis, A, and a third portion extending transverse to the principal axis, A, and being engaged with the engagement element, wherein the fastening element is configured to clamp the first portion between the flange and the housing in a direction parallel to the principal axis, A, and to clamp the second portion between the housing and the flange in a direction perpendicular to the principal axis, A, and wherein the third portion, via the engagement element, is configured to press the reflector towards the lid element.