The gas inside the Reddit user's tube seems to be xenon, ... like a wall socket, rather than a Tesla coil. This is exactly what happens in neon signs and fluorescent lights.

The fluorescent tubes used to light offices use "hot cathodes,"-coils of wire coated with materials that enhance ther-mionic emission, or the "boiling off" of electrons, to generate their plasmas.

Fluorescent tube lighting was a staple in homes and commercial buildings in the late 20th century. In residential settings, it was especially popular in kitchens and can still be found in older ...