Abstract: An immersion lamp for a photochemical reactor with a discharge tube fitted in an outer bulb through which an inert gas flows having a lamp bulb with axially opposite mechanically stable electric terminals is held and contacted in a holder in the outer bulb, and the outer bulb is tubular and has at least one open end projecting into a hollow space in a connector head to provide electric contact and a secure mechanical support; the open end of the outer bulb is surrounded by at least one elastic seal which is surrounded axially by two inelastic metal plates laid on it having cut-outs for the passage of the end of the outer bulb and screws; the pressure exerted by said screws deforms the elastic seal radially to such an extent that it seals against both the outer wall at the end of the outer bulb and the inner wall of the hollow space and secures the outer bulb centrally in the connection head.