Summary

3 different lamp shades

• Facetted diffusor
• Isocahedron diffusor
• Dodecahedron diffusor

The faceted diffusor (shown in the photograph) was printed upside down. Prusa slicer complained about collapsing overhangs but did print fine. I chose a 0.12 mm layer size with a 0.4 mm nozzle to give it sufficient overlap between layers. The filament used was transparent PETG, which becomes translucent when printed.
The two parts have to be glued together with superglue. Also the light bulb needs to be glued in place with a few drops. Keep in mind that the hole in the diffusor is 33mm in diameter. You might need to cut it slightly bigger with a sharp knife or change the design, depending on your light bulb.
SketchUp design files are included.

I did not print the Isocahedron and Dodecahedron myself (yet) but I expect no slicer warnings because these have less overhang. Please let me know how they print.