In a light-tight enclosure, elongate members and joint connectors are joined to one another to form a framework to which panels having projecting ribs with right-angled corners are mounted. Each elongate member is extruded from aluminum so as to have open ended grooves. Each joint connector is fabricated from aluminum so as to have open ended grooves, some of which have right-angled corners conforming to right-angled corners of the projecting ribs. At each joint where elongate members and a joint connector are joined, the open-ended grooves merge with one another so as to define continuously extending grooves receiving the projecting ribs of the panels mounted to the framework at the joint. Some joint connectors are employed as corner connectors while other joint connectors are employed as edge connectors.