| With MV there is not much room to gain in efficacy, eventhe normal probe start are near the attainable maximum.
The omission of the probe is important only when you need to reach higher operating temperature of the fill, what is necessary for only MH.
MV are still operated way below what the probe design allows, so no benefitt to complicate the ballast.
The probe start MVs didnt make it to Europe (except some early experiments) because they need higher ballast OCV for reliable starting and operation. In the US this was no big deal, as the ballasts have to be already an autotransformer, so increasing the OCV makes no extra trouble. But in Europe (and all 230V world) the MVs sufficed with just a series choke (well, their electrical specs were intentionaly designed so, because just a choke costs half, weighs nearly half and has half losses compare to a transformer basedballast). To suffice with just 220V OCV, they had to reduce the arc voltage, so increase the current. But that means the burner became shorter and thicker. With that, the wide seal necessary for the starting probe would obscure too much light and dissipateway too much heat (so make the already tight thermal budget even tighter), the lamp efficacy would be too low. Anddont forget, the probe brings reliabiliry problems into MH too (when voltage present between theclose spaced electrodes, the MH environment yields severe electrolysis corrosion, so a switch had tobeused to short the starting probe to the main electrode, so extra complication and extra issues; the puremercury inMV is quite inert, so no such problems in the MV).
To start the lamp without so much arcvoltage reduction needed some voltage boosting, so an ignitor. And when the ignitor was present, it was not much extra complication to make the ignition pulse high enough, so the troublesome starting probe could be omitted.
But in recent years, pulse start MV was brought to the market: Because of the MV ballast ban in the US, EYE lighting (Iwasaki) introduced an MV lamp designed to operate on a pulse start MH ballast, for applications requiring clear MV light color. Because it was designed to operate on a ballast generating HV pulses, the internal construction need to assure sufficient dielectric strength (except the arc cavity itself, of course). Andthat means the starting probe and its resistor had to go away, as they would become the weak point there.
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