UPDATE 6/20/12: Added Netfabb'ed versions.
This is a press-fit lamp shade for inexpensive 12V 9-LED T10 automotive lamps. I believe these are sometimes called "wedge lights," and are used as turn signals or interior lights. (I got mine on ebay for $1.50 for two, shipping included.)
They're made for 12V DC operation, which is convenient for reprappers, and they don't really need to be fastened to the frame if you're using solid core wire.
These things are quite bright, and the shade does a great job of keeping the light in one place and not in your eyes. They require about 225mm of 3mm filament each (about a nickel).
v1.0 - The original prints shade down, with no built-in support structure
v1.1 - Prints base down with extra support on the shade-to-base transition. (On left in photo printed in white.)
v1.2 - Prints shade down with simple built-in support structure. (On right in photo printed in white.)
1) Print the part. (Check description above for which version to print.)
2) Strip about 4mm of the ends of a wire (I use twisted pair from old network cable), and insert the bare wire into the holes on the side.
3) Noting which side is positive, press the bulb into the slot and be sure the wires are pressed toward the back and are not shorted.
4) Plug it into to a 12V and aim it somewhere interesting.
I created this with OpenSCAD and printed it with yellow 3mm PLA withh a 5mm nozzle on a self-sourced Prusa Mendel. I had to clean up the inside a bit, but other than that it seems to work just fine. Enjoy!
I need to clean up the OpenSCAD file a bit -- it was a bit of a quick hack, because I just received the lamps today -- but I'll post it when I do.