How fluoro tubes start is a bit complicated.
Initially the glass tube contains a low pressure unionized gas. The gas atoms have all their electrons, so don't get accelerated by electric fields.
There's a parameter in a gas called 'mean free path'. This is how far atoms can travel before hitting another atom (not counting the walls.) It's important because this determines how well an electric field couples to charged atoms. They accelerate in the field, but the energy (velocity) they can reach is limited by how far they can travel in the field before they hit something and lose a lot of their energy. (For the moment, ignore that moving charged particles themselves alter the electric field.)
This applies to free electrons too. In a uniform field they accelerate till they hit something, and share their kinetic energy with the other thing (gas atom etc.)
Air at STP is a good insulator because it takes very high E field to accelerate ions or electrons enough with their very short man free paths, to achieve an ionization cascade. Very low pressure gas is easily ionized since the mean free paths are long (mm, inches, meters, light years ha ha) and even low E fields can impart enough kinetic energy to ions, to cause every impact to produce more ions.
There are two types of (pre-inverter) lighting fluoro ballasts, one uses a starter, the other doesn't. But both try to do the same thing - get an arc started in the tube, then limit current to a suitable level.
This requires:
1. Get the filaments hot enough to emit electrons.
2. Have enough electric field around the filament surface to make electrons leave the metal surface.
3. Have enough field strength in the gas around the filaments, for the electron's mean free path to allow them to pick up enough kinetic energy, that when they hit a neutral gas atom they will ionize that atom. (ie knock off one or more electrons.)
If that all happens the tube will have an ionization cascade in the vicinity of the filaments, and the resulting charged particles (electrons and atoms, ie plasma, which is very conductive) carry an intensified charge gradient down the tube to the other end (or meet a similar gradient coming the other way.) Once the entire tube is full of plasma there's very little electrical resistance between the ends, ie not much electric field can exist anymore. The tube will carry whatever current the ballast allows. (This ignores a whole lot of more complex plasma behaviors, like double walls, Birkeland currents, magnetic effects, velocity waves, etc, but fluoro tubes are optimized to mostly avoid such effects.)
So the early phase of tube startup depends on field strength around the filaments. Early battens had grounded metal spring contacts that earthed the metal end caps on the tubes - which are close to the filaments. This helped. Same as someone mentioned wrapping a grounded foil strip around the tube. Another technique is to have a grounded strip on or close to the tube, whole length of the tube. This has also been a commercial technique. Cost cutting removed all these.
Remember that while the internal gas is neutral, the electric field inside the tube is solely determined by the charges on objects - filaments, end caps, batten body. The glass doesn't act 'capacitively' (much) because there are no free charges to accumulate on the inside of the glass, restricting the field endpoints to the inside and outside of the glass.
Once the gas is ionized, it's a completely different system. The field inside the tube is entirely dependent on the filaments and current, because there are free charges that flow to neutralize external fields.
Tube 'aging' is due to diffusion of extra gas into the tube, decreasing mean free paths. This makes the tube require higher electric fields to start, and also ultimately makes it unable to sustain a plasma.
Humidity has an influence because water molecules adhered to the outside of the glass form a somewhat conductive film, also in contact with the metal end caps. But it's not grounded, so can float to some average. This tends to reduce the local intensity of electric fields around the filaments while the gas is still neutral. Hence making it more difficult to achieve the initial ionization cascade. Unless you touch that film, which changes the average voltage since you added your body capacitance to free space even if you are not earthed.
Even in dry air, putting your finger on or near the tube ends can assist starting, for the same reasons.
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