Retrofit fluorescent lighting fixtures for installation into a surface mounted cylindrical lighting fixture of the square or cylindrical shape. A 4-wire assembly is used for replacing conventional incandescent light bulbs with fluorescent light bulbs in existing lighting fixtures recessed downlights, in particular. The retrofit lighting fixtures include, inter alia, a threaded connector, a ballast, a heat exchanger, a fluorescent light source connector and a threaded body for receiving a reflector glass.