A lamp subassembly includes an air-tight plate, a mounting lamp holder coupled to the air-tight plate, and a mounting spring coupled to the air-tight plate and the mounting lamp holder. The lamp subassembly is coupled to a trim with the mounting spring and coupled to a lamp with the mounting lamp holder to form a lighting fixture. The air-tight plate is coupled to a top opening located on the trim and forms an air-tight interface therebetween. The mounting lamp holder positions the lamp at least partially within the trim. The air leakage through the air-tight interface is equal to or less than two cubic feet per minute at a seventy-five Pascal pressure difference.