How to do it
How to Work with a Suspended Ceiling
To replace a fluorescent fixture in a suspended ceiling, shut off power to the circuit. Remove the ceiling panels around the fixture. Remove the diffuser, disconnect the wires, unscrew the locknut, and pull out the cable. With a helper lift the old fixture out and set the new fixture in place in the ceiling frame.
If you're installing a fluorescent fixture in a suspended ceiling, clamp the cable and splice the wires, as in Steps 3 and 5 above. Replace the ceiling panels, install tubes, and slip on the diffuser.
Open Knockout Hole
How to Install a Circular Fixture
A round fluorescent fixture usually mounts to a box. Thread the house wires through the hole in the middle and splice them to the fixture wires. Start driving both mounting screws into the electrical box, then tighten.
How to Install a Fluorescent Fixture Mounted to an Electrical Box
Sometimes fluorescent fixtures are mounted to an electrical box. In this common arrangement a nipple (short threaded pipe) and the wires poke through a hole in the middle of the fixture.