The Borg transponders had a clear acrylic rod at the top and had a light defuser inside around the "perf" tube as Penny called it. She said it was the protective sleeve for fluorescent tubes, but i've also been told its industrial paint mixer.
The tubing can be seen in many places. Anthony used a ton of it in busy boxes. as well as part of the warp coils.
The bird feeder was also seen used as a high speed rail system at Starfleet Command.