Abstract: A lamp unit for use within a socket which defines an opening having a pair of upstanding walls. The unit is especially adapted for use in projection applications, e.g. movie, slide, and microfilm projectors, and comprises a base which is positioned within the socket's opening, a reflector and electric lamp securedly positioned within the base in a coaxial relationship, and biasing means in the form of an elongated rib, two spaced protuberances, or a resilient spring, etc. located on one side of the base. Accordingly, the base is biased against one of the upstanding walls of the opening to provide an interference fit between base and socket and maintain consistent alignment of these components. A lighting assembly utilizing the above lamp unit is also disclosed.