I was recently at the Nikola Tesla Museum in Serbia. I found it a bit lacking on the science aspects of Mr Tesla - but it held a remarkable collection of his personal belongings (he was evidentially an exceptionally well-dressed man).
Anyway one of their exhibits was a Tesla coil which discharged to a grounded sphere (on the ceiling). People were asked to hold fluorescent tubes which glowed. See image from the museum website.
The explanation given at the museum was that the electrons from ionised air travelled down from the "lightning" to the tube, completing the circuit and thus the tubes light up.
Reasons why I think the explanation may be flawed:
- The mean free path of electrons is too small in air to travel to the fluorescent tubes. I haven't done the calculations - but I have a feeling of it being on the order of nm to cm - not metres as is required.
- The "turn on" was instant when the lightning started - this suggests, for me, that something with the E field is much more likely than charged particles.
- Electrons would ionise the air before travelling to the tubes.
- The ions/electrons and plasma would be contained very close to the lightning (this is really a restatement of the above points).
So, does anyone have a better explanation?