The ballast is designed to last 10 years, and there is an underlying assumption (which is not always correct) that it is not stored for too long from manufacture to when it is put to use

The PME's will last 10 years, the problems with them start sometime at 20 years or older

Plastic film caps with the minimum voltage ratings (typical 275V) may fail already within the 10 years. The capacitor locations in the ST ballast don't suggest that they are EMI capacitors - They may be things like DC-link or even in the lamp circuit, although the type of capacitor does suggest EMI (all other capacitors in the ballast are not in X or Y positions, so typically manufacturers use there capacitors without X or Y ratings)

If then we ask why a bit higher voltage rated caps are not used, that's because the manufacturers don't deem it necessary to overdo if it seems to fit by ratings

(And hey, the electrolytic cap is typically rated for 15 years from the date of manufacture, as an additional limit besides the hours rating)

If they would want a ballast that is likely to last "unlimited" life, and assuming the manufacturer's engineers are aware of the PME failure mechanism, the capacitors would be indeed some plastic film but with 1.5x+ voltage ratings, which would also be bigger in size

In few cases a PME may also last for many years beyond the 20 year line, if it is working in conditions that prevent the failure from happening (see Perfektstart example). I don't think it was intentional (or that the failure mechanism was known at all) back when those Perfektstart ballasts were designed, but nowadays if a PME is used in a similar way, it may not be a significant limiting factor in the ballast's life. (HF ballasts are not enclosed enough, and dont have components that get hot enough for this to work for them)

And, you may be surprised how much common knowledge of us electronics amateurs (and those of us who became engineers) is completely alien to absolute most of engineers working in design of devices. This goes well beyond being familiar with failure modes of some components

I am in possession of a 3600V 8mA neon sign transformer. This means it has peaks of a bit over 5kV, which is around the voltage of an electronic ignitor. This transformer can run 24/7 with a dead shorted secondary, and just get a little bit hot. This means I can safely put just about anything across its output. It also has an isolated secondary, which is important. Here is my plan for making this into a universal HID lamp ignitor:

For this explanation I will separate the secondary leads of the neon sign transformer into H1 and H2 just for clarity purposes, though there is no practical difference between the two.

- Connect the COM wire from the ballast to the socket's neutral connection (as per usual)
- Connect the H1 wire from the NST to the socket's neutral connection
- Connect the H2 wire from the NST to the socket's live connection
- Connect the LAMP wire from the ballast through a high-voltage tolerant switch to the socket's live connection

1) Starting with the high-voltage tolerant switch in the OFF position, power is applied to both the NST and the HID ballast. This strikes a low-current arc through the discharge tube of the lamp.

2) With the arc struck, the switch is then flipped to the ON position, applying the ballasted output of the HID ballast across the lamp (and also the secondary of the NST, which should be able to handle this at least temporarily). This ballasted output applied across the transformer would essentially just short it out, which is ok because it seems to have no complaints about being shorted.

3) Now with the arc properly struck, the NST is doing practically nothing, so its primary may be disconnected.

If I had access to a PSMH or HPS lamp I would try this out, but I own neither of those types of lamps. Do you think this would work? Obviously you might have to try flipping the switch a few times depending on what part of the AC cycle you flip the switch, but I think this would work. Ideally the NST wires and ballast wires would be phased so they are both positive and negative at the same time, but I don't really think that would matter if you got it the other way around. I could be wrong though. What do you think?

Shouldn’t be a problem in your enclosed fixture?, although it would be sad to loose the lamp prematurely? 🤔

Over here, the low floor city busses in my city have blue lights in the front that are dimmed when driving but come on when stopped, the lights at the back are just normal white. I believe this is done to keep the drivers night vision.

I thought of this thread a few weeks ago, when it started getting lighter later in the morning. I was sitting at a stop sign behind two school busses, and both had the interior lights on while moving down the street and at the stop.

@Ash, yes usually they transfer the fixtures here as well, even if they aren’t used anymore. There is an OLD mercury  GE M400 at the Enterprise here (was an old gas station) that hasn’t worked in a few years, when the pole was replaced, they transferred it anyway.

@BT25, most of the ones here aren’t installed on a separate pole either, my next door neighbor used to have two HPS NEMA heads requested by a previous owner. When they stoped paying, the PC were removed. When a new house was built, they removed the one from the transformer pole to install an underground feed. The other fixture was on a separate pole, and remained for a few more years until the current owner had a steel garage built in that spot, so the power company removed it and the pole. I was at work when the work was performed, I wish I’d been home since maybe I could’ve gotten the fixture and arm, being they weren’t going to be used anymore.

@HomeBrewLamps, I’ve seen that here too actually. There was a GE M250R2 at a house that was demolished, but the fixture was never disconnected and still had power. Although the HPS lamp started cycling. I doubt they ever disconnected it, but I haven’t been by that way after dark lately.

Thank you for providing this invaluable resource, @Olav . 

The point was to use it not for measurement, but for calibration while still staying on DIY budget. For calibration the jitter is way less critical, the only thing it impacts is the time how long you need to compare the signals.
With any stand alone instrument you will always face a question whether it still works. With radio reception also carrying the timing standard you have that information: Either it is locked, so accurate, or ot is not locked and then you know that.
With GPS you know that - either it reads your position correctly (then it is clearly locked; assume you know where you are so are able to verify that), or not (so then it does not work at that moment).
Also with the analog TV: It either showed correct image, then it must have been locked, or it was not.

Of course, any radio based timing signal distribution does suffer from jitter, that why it could be using just for calibration of some more stable and cleaner generator. In that respect the GPS provides still the best quality signal, compare to other methods available for similar money.

I hope this don't increases the risk of an arctube explosion?

Interesting 🤔, maybe the environment they were made in wasn’t as pure as it was with European manufacturing?, and airborne particles stuck to the tube when still hot from moulding?
I haven’t seen this before?