Flat Light Covers
Purchase a 2 by 4-foot acrylic fluorescent light cover. The universal size of this light cover fits nearly all 4-bulb fluorescent troffers.
Hold the flat cover at an angle and slide it into the troffer if your fixture has a decorative box around it. Bend the cover slightly to get the cover to fit past the lip of the troffer if necessary. Release the cover to sit flat against the bottom of the fixture.
Open the 4-bulb fluorescent light fixture if a thin metal frame secures the cover in place. The frame secures to the fixture with small screws or metal tabs that lock the frame to the fixture.
Lay the 2 by 4-foot acrylic light cover into the frame. Close the frame on the fixture and secure it with the screws or metal tabs.
Trim the acrylic light cover to fit your 4-bulb fluorescent fixture if necessary. Measure your fixture, then transfer the measurements to the flat acrylic cover. Run a plastic sheet cutter along the light cover 7 or 8 times to score it. Use a straight edge to keep your score lines straight. Place pressure on either side of the score line to pop the acrylic apart along the score line. Install the trimmed fluorescent light cover into the 4-bulb fixture.
Wrap-Around Light Cover
Take the original wrap-around 4-bulb fluorescent light cover with you to a lighting supply store or home improvement center if you have it. Take measurements of your fluorescent fixture if you do not. Measure the width, length and depth of the fixture.
Match your original cover to a replacement cover for shape and size at the lighting store or home improvement center. Confirm that the replacement cover will fit your fixture's measurements.
Install the replacement wrap-around light cover onto your 4-bulb fluorescent fixture. Hook the side of the cover around one side of the fixture. Wrap the cover around the fixture and hook the opposite side of the cover to the opposite side of the fixture. Since wrap-around covers are not universal, you may need to contact the manufacturer of your fixture for a new cover if the cover you purchased does not fit.