Buy the galvanized pipe and fittings from your local hardware or plumbing supply store. The store personnel will cut the pipe to the desired length and thread the ends for you if necessary. Assemble your tools.
Lay the pipe and fittings on the floor of your work area. Screw one end of each nipple into a flange. Screw the other end of each into an elbow. Tighten with a couple of pipe wrenches; it doesn't have to be real firm. These are your bracket assemblies.
Screw one assembly onto each end of the long pipe. Firm them down with the pipe wrenches, making sure that each assembly is in line with the other. What you should have is one very fat "U" shape. Stand the assembly on the floor using the flanges as feet and adjust the tightness of each elbow until the assembly stands evenly flat on both flanges.
Climb a ladder with a pencil in your pocket and one end of the light bar assembly in one hand. Have a helper do the same at the other end of the assembly. Hold the flange to the mounting position and mark the screw holes of the flanges on the mounting face.
Note: Your light bar must be mounted into a solid surface such as a glue-lam beam.
Descend the ladder and lay the assembly on the floor. Climb the ladders again and drill 1/4-by-3-inch pilot holes into the mounting surface at the pencil marks.
Climb back down the ladders and retain the light bar assembly along with four lag screws and your ratchet. Head back up and place the flange against the mounting surface. Position your shoulder against the bar to hold it to the surface.
Place a lag screw in the first flange hole and ratchet it down. Ratchet a lag screw into each of the other holes. Firm them up and you're done. Now you're ready to hang lighting instruments from the batten.