Based on the generic shape of Andrewar's c7 cover at http://www.thingiverse.com/thing:9719 this was designed and sized to fit on the common 12mm Pixels and dumb LED's used in many Christmas Light displays, and more specifically my display.
This cover is 55mm high and 24mm in diameter and is a firm fit on the pixel. Printed with 2 layers for strength, and additional support at the join of the base and light, this should last well outside for the Christmas display time here in Australia.
The demo was printed in White ABS, but the final versions will be printed in natural ABS, with a layer of Krylon clear UV protecting spraypaint to keep them looking fresh for a few years to come.
2 layer walls, 2 layer base and 3 layer top. 0.2mm layer height and 60mm/sec speed (But can go faster with no problems), 100% infill, but I think there is only 1 or 2 layers at the transition of base to lamp sides which are filled, and no supports needed at all.