How to Cut a Plastic Diffuser for Fluorescent Lighting

When you install a wood enclosure around a fluorescent light fixture, you will often need to cut a plastic diffuser to fit over the enclosure opening. Due to the nature of the plastic material used in the production of the diffuser, you will have to avoid the majority of power cutting tools. The design of power cutting tools requires teeth to cut through material. If the teeth of the power saw grab the brittle plastic diffuser, the plastic will crack and the diffuser will become unusable.

1. Measure the inside length and width of the wooden fluorescent light enclosure to make sure that you need to trim the plastic fluorescent light diffuser and then measure the length and width of the enclosure opening.

2. Determine the length and width that you need the fluorescent light diffuser. You need to make the diffuser small enough that you can slip the diffuser through the opening of the wood enclosure and large enough that the diffuser cannot slip through the enclosure opening.

3. Place the 1/4-inch plywood on a flat surface at a height that will allow you to work comfortably.

4. Lay the plastic fluorescent light diffuser face up on the 1/4-inch plywood.

5. Mark the length and width you determined in step two on the face of the diffuser with the felt tip marker. You will need to place two corresponding marks for each cut to align the straight edge.

6. Cover the area around the cut marks with masking tape to protect the surface where you will place the straight edge.

7. Align the straight edge on the corresponding width marks that you placed on the face of the diffuser in the previous step. Do not slide the straight edge across the surface of the diffuser, as this will create scratches on its surface.

8. Maintain pressure on the straight edge with one hand to keep it from moving during the cut and place the utility knife on one edge of the cut, with the knife blade resting flat against the side of the straight edge that you intend to cut.

9. Slowly pull the utility knife along the straight edge while applying downward pressure to the knife. Repeat the process until you have a score line 50 percent of the way through the diffuser.

10. Remove the straight edge from the surface of the diffuser and place the diffuser on a flat surface that has a square 90-degree corner. Do not attempt the next step on a radius corner.

11. Align both ends of the score mark with the square corner and the piece of the diffuser you are removing overhanging the corner.

12. Hold the diffuser in place with one hand and place your other hand on the edge of the diffuser overhanging the corner.

13. Apply pressure down with your hand on the piece of diffuser extending past the corner until you hear a snap. Move your hand along the edge applying downward pressure as you move to separate the pieces of the fluorescent diffuser.

14. Remove the masking tape and then drag the sharp edge of the utility knife blade along the cut edge to remove rough edges from the cut edge.

15. Repeat the process if you need to cut the fluorescent diffuser in the opposite direction.