Abstract: A luminaire has a captive stop slidable in a track in the lamp housing, the stop being engagable in bayonet fashion with a recessed track on the light source support housing insertable through the rear of the lamp housing. This permits the axial position of the light source to be set and maintained even when the light source is removed e.g. for replacement. To permit radial positioning of the light source, a pair of plates are constrained to slide in orthonal directions by pin and slot mechanisms, and a bolt is arranged both to displace the plates, and to lock the plates together at the desired radial position. A screwdriver is insertable through a hole in the lamp handle, to engage the bolt, and to give radial leverage in adjustment.