Things You'll Need
Ceiling wire hanger screws
Installing lighting into a suspended ceiling is simple if you use specialized 2-by-4-foot fixtures. These fixtures take the place of a ceiling tile, and by exactly matching the grid, they don't require any modifications to the grid or ceiling tiles. Since the fixtures weigh considerably more than does a standard ceiling tile, they must be self-supported to the structure above to prevent damage to the ceiling grid or falling out of the ceiling and causing injury.
Turn the power off to the circuit that will be feeding the lights. The easiest way to do this is to turn the associated breaker in the circuit breaker panel to the "Off" position.
Hang four ceiling wires down from the ceiling structure -- one at each corner of where the light fixture will sit. The wires should extend about 6 inches below the bottom of the ceiling grid.
Tilt the light fixture at a slight angle, lift it up through the ceiling grid and slowly lower it into the grid. Maintain slight pressure on the bottom of the light so the ceiling grid does not bear its full weight.
Start at one corner of the light fixture and bend that corresponding corner's ceiling wire up and through the eyelet on the light fixture. Pull tight and twist the wire around itself. Repeat on the other three corners. The light fixture should be entirely supported by the ceiling wires and will barely rest on the ceiling grid.
Insert the wire whip from the light fixture into the nearby electrical box that serves the lighting circuit. Tighten the connector nut to hold the whip in place.
Twist the black wires together, the white wires together and the ground wires together. Secure each grouping of wires with a wire nut. Screw the cover back on to the electrical box.
Follow the above process for each additional ceiling light. Once complete, restore power to the lighting circuit and verify that the light fixtures work properly.
Installing the light fixtures before tiling the ceiling is much easier. This will give you many access points to work above the ceiling on the light fixtures and their associated wiring.