Abstract: A rectangular reflector sheet of relatively stiff aluminum is curved into the general shape of an elongated parabola and is inserted into a cylindrical transparent glass tube so that the edge portions of the sheet press outwardly against the tube. A set of end closure caps or members are clamped against the ends of the tube by a pair of tie bolts which extend axially between the reflector sheet and the inner surface of the tube. Each of the end closure members is provided with an annular groove which receives an annular resilient gasket and the corresponding end of the tube to form a fluid-tight seal between the tube and the closure member. One of the end closure members has an eccentrically located hollow hub portion which supports a socket for receiving the socket end of an elongated lamp element extending along the offset focal axis of the curved reflector sheet.