Be sure to fix the cigarette lighter.

I also know that a Kovar alloy was used for most hard glass SOX discharge tubes, were they ever made with the harder ~3.3e-6 borosilicate and tungsten?

There is no single way how a HP Fluorescent circuit can be implemented, and each circuit will behave differently. Some possible behaviors may include :

The lamp current going down as the capacitor value is going down, while some other current draw in the circuit (the filament heating, the ballast primary winding losses, etc) remains unchanged. So while the phase angle of the current component affected by the capacitor may be going more and more like 90deg (towards capacitive), at the same time its effect is becoming less significant for the complete ballast PF which is seen from the line outside, so the PF of that one stays high

The lamp current not changing, but ballast primary current is rising and along with it the ballast's resistive losses, which pull the PF towards unity. Within some range of capacitor value (as it is failing), it is possible that the change in PF (towards inductive) is masked by the increasing "resistive" component of the current

The capacitor is parallel to the line input, and not actually part of the ballast circuit (even if it is hidden inside the ballast enclosure). The change in PF (towards inductive) will be clearly visible

Will a ballast with a capacitor that is going bad have a lower PF?

I had one that even when it was showing signs of failing had a near perfect PF (0.99)

All luminaires compared are ceiling installation, and all really have no diffuser or any type

The Fluorescent ones with bare tubes (36W T8 or 54W T5) are installed flat on the ceiling, at about 2.5m height

The LED ones with bare visible individual LED dies are often in the form of dangling chandeliers, those are often installed in newer houses with higher ceiling, but the actual light emitters are hanging at about the same 2.5m

Many of the LED ones are only counting on isolated LED drivers for the safety, some are questionable at that too (output Voc exceeds SELV limits, bad clearance distances on the PCB or inside the transformer insulation are common)

The car the Blue Brothers drove.

Yep, this 1974 Dodge Monaco

When the further or higher the fixture is, or the higher the general illumination level is, the higher intensity gets acceptable. This has never changed. And installations using indirect lights are not "bare tubes" from this perspective (when the tubes are not in the direct view).
But there were many installations like bare tube lights on a wall behind a bench at the eye level or so.
There the bare tubes are too bright. But if you put them above, there is no problem.
Of course people adopt to what became available: If low brightness tube ballast were available, placing two bare tubes directly on the wall became the easiest and cheapest thing, even when they are in the direct line of sight.
When not (like for the T5's), a fixture with a single tube and a refractor to spread the light over larger area was chosen. The higher price and the need to clean it from time to time accepted as a fact of life, when there was no other choice.
Or it was not installed on the wall, but onto some brackets or hung higher above the desk, so it was not at the eye level. Again a more complex and expensive setup, but if you have no other choice...

By the way in these applications this is the reason the T5's were in fact not more efficient than even T12: T8 or mainly T5 required a refractor, which absorbs a lot of light, so you need higher lumen light source to compensate for the losses. With a T12 tube, which could be run bare, the less losses means less lumens are sufficient, so even with the lower raw efficacy of the lamp the overall consumption becomes comparable.

LEDs can not work without a cover for electrical safety reason, but there is quite wide range of intensity to select from, so you use the lantern that suits the need. But the advantage of LEDs is, their lifetime allows to make the refractors sealed, so rather immune towards dirt accumulation on the rough side of the refractor (where the dust tend to stick and becomes difficult to clean out). Plus the LEDs do not expose the plastic to the UV, so there is wider selection of or less restriction to materials for it, so it could become cheaper.

Then what changed since then which made bare T8, T5HO and now LEDs acceptable ?

The F40 at full power has about the same intensity as the F20, but that is too much for some applications.
The lower intensity of the F40 operated at 25W was used not as a replacement for GLS, but more like equivalent of the linear incandescents used in Europe.
The refractors were used with incandescents, with classic bulb format there was no other choice, but they always had those disadvantages.
Using bare tubes operated at lower brightness meant just a cheaper, simpler and even more efficient way of getting similar result and getting rid of those disadvantages.

In Europe in a "progressive energy efficiency" legislation was formed (somewhere in the 60's till 70's) banning all gear that operated the lamps at lower than rated lumen output, effectively banning an equivalent approach in Europe. Not that European market wouldn't want similar solution, but it was the bureaucratic legislation written by activists what stopped that.
So way less efficient linear incandescents were used instead. It made money for the lamp makers (the lamps were very expensive; so the lamp makers were happy) and consumed way more power (nobody cared), but did not violate the standards (that is what the bureaucrats cared). The modern "energy efficiency standard" laws are nothing new in their stupidity...

I recently obtained this fixture that uses 4 13w PL bulbs, however the ballasts it came with are extremely loud and seem to heavily overdrive the lamps. The current ballasts are Robertson model SP2, which I will add an image of. Anyone know of quiet ballasts that would properly drive the lamps and that I could obtain at least 4 of? Thanks.


Here is a video of the fixture operating, showing the noise.

https://www.youtube.com/watch?v=MBGkSB_3NkI