| I think the main reason is, then lamp with arc voltage less then the 1/2 of the ballast OCV. So if the lamp arc voltage is below half of the mains one, it then suffice with simple, quite small and rather lightweight, at the same time quite efficient serial reactor ballast to maintain the arc, so in the glowbottle starter preheat circuit to incorporate the start.
If the lamp require higher arc voltage, it need a transformer to boost the OCV of the ballast up. And once you need the transformer and so are ready to swallow it's mass and losses, more complex starting schemes may be used, include the RS.
As the US mains is only 120V, for all lamps of 30W and above it does require the transformer, so it is then mostly implemented in the form of RS ballast, to get rid of the starter.
Note, then for smaller lamps (22W and below) even in US newer RS ballasts are very rare and in most case series chokes with the starter (or even manual switch) preheat circuits are used.
In contrast in EU (and i guess most other 230V countries) the series choke is sufficient for nearly all lamps (lower voltage lamps may even work in series pairs on one ballast), it is impossible to beat the efficiency, mass and the reliability of this setup by more complex, heavier, lossy and costlier RS (include those "resonance start") setup.
The only drawback of the glowbottle preheat is the delay and flashing on the start, what was more targeted by electronic starters working along programmed start lines (first preheat only, then apply starting pulses with continuing heating), what keep all the benefits of the preheat setup.
These starters didn't find their way to US, as they were of rather high complexity (electronic devices) compare to already proven RS setups and came quite late - when way more efficient electronic HF ballasts already start to appear.
And these days even the series choke is treated as inefficient (mainly due to higher efficiency of the low pressure discharge at higher frequencies), HF electronic ballasts start to "rule the world".
But even there are significant differencies between US and EU with otherwise similar cheap instant start ballasts:
- US tend to short out the filament and connect the lamp only using two wires. I guess the main reason is the wiring simplicity in the fixture and the fact, then the filament does not have to be really intact for the lamp to operate. The starting resonant capacitor is then connected parallel to lamp wires inside the ballast. This have the consequence, then the high voltage is present even with removed lamp, so if the new one is replaced connecting the "hot" end first, it may ignite it and let the current to flow to the man replacing the lamp, causing usually burns (the frequency is usually high for nerves to respond and to even penetrate deep enough due to surface electromagnetic effects, so does not cause the shock, but it still heat up the skin surface, so still may burn it). Second drawback is, it require special EOL protection, as if the lamp totally fail, it stay in the highly stressing "ignition" mode for long time, what mean necessity to use way higher rating of used components. And even this is frequently not sufficient to protect the ballast.
- EU even on simple instant start ballasts use 4wire lamp connection, while the starting capacitor is connected in series with filaments. The behavior is the same as the US connection, as the high voltage strike the lamp way earlier then the filament temperature may even change a bit, but such connection make the setup sensitive to both filament's integrity.
I think this sensitivity is assumed as rather benefical feature, as it provide few handy safety services:
-It start the ballast only, when all connections are complete, what mean no potentially live parts may be touched. I guess this is required by the code in EU.
-Removing the lamp shut the ballast down, allowing safe relamping when power is ON without causing stress on ballast components.
-The filament serve as an EOL fuse: When the electrode loose emmissive coat, the arc voltage rise, what cause elevated current in the starting resonance capacitor. As this elevated current flow trough filaments, it overheat them, causing them to evaporate and break. And as the ballast is not able to work with broken filaments, it shut down by itself, protecting it's components from overload damage, so it stay operational, once the lamp is replaced.
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