The invention relates to a watertight lighting module comprising a substantially cylindrical translucent housing, a support structure that is to be placed in the housing and that is provided with contact terminals and current conductors for an electric lamp, a closing arrangement for the housing with the lamp and the support structure placed therein, which closing arrangement has a seal of elastic material capable of sealing off the contents of the housing from the environment in a watertight manner when pressed against said housing, wherein the closing arrangement comprises an elastic ring and cooperating pressure-exerting members that act on the elastic ring such that said ring is radially stretched so as to form a watertight seal against the housing; more in particular, such a lightingmodule in which the cooperating pressure-exerting members constitute two clamping parts which are mutually movable, which extend conically, and between which the elastic ring can be clamped in such that said ring is radially stretched, wherein said conically extending clamping parts can be displaced relative to one another by means of a setscrew so as to stretch the elastic ring radially through a tightening of said setscrew in a screw thread at one of the conically extending pressure-exerting members in the direction of the other conically extending pressure- exerting member.