Polishing the edges serves a dual purpose. Polishing the top and side edges is aesthetically pleasing and on the other hand polishing the bottom edge will allow more light to be transmitted by the LED’s.
1) Sand edges. Use progressively finer grit sandpaper starting at 220 ending at around 600. For best results finish with 800 grit sandpaper. Be careful to not scuff the front or back sides of the sheet with the sandpaper and try to maintain an edge that is perpendicular to the front and back sides.
2) Clean edges. Gently wipe with wet towel and dry.
3) Heat edges until clear. Use a concentrated heat source to heat the edges of the polycarbonate to a high gloss finish. Heat sources can be heat guns, lighters, or mini blow torches. You can over do this! Take your time working slowly along the edge close enough to barely melt the sheet.