These MV-ballast retrofits are going to be banned in 2015 due to their low efficacies. But what makes them low? Is it an internal ignitor presence or a different chemistry making them MV-ballast current compatible...?
And why on earth there's a strange efficacy drop just with a 110W version? (see a pdf catalogue from Osram.com).

NAV-E 68W - 82 lm/W
NAV-E 110W - 73 lm/W (!!!)
NAV-E 210W - 86 lm/W
NAV-E 350W - 97 lm/W

(If you browse Osram.com/HIDs - this 110W Plug-In is already missing in their catalogue - it seems they are selling just 68W, 210W and 350W versions.)
Note: Similarly looking NAV-E 100W (non-retrofit) has much better efficacy of 91 lm/W.

The efficacy is lower due to the diferent buffer gas fill. And yes, the reason is to make it compatible with MV ballast - the "starter" ignitor do generate the HV pulses with just a series choke, but that mean the ballast coil is exposed to the high voltage pulses. And that could be a problem, mainly with older ballasts with worse internal insulation of ballasts designed just for MV (MV does not generate any high voltage at all).
So therefore for a retrofit purpose, the lamp should live without any HV pulses at all, so they have to suffice with just easy to ignite penning mixture for the gas fill and starting antennas. And the Neon there is the cause of the lower efficacy.

This is the main difference between selfstarting HPS, which use the internal ignitor instead of the Penning mixture gas fill. But the HPS ballasts are expected to be designed so, they could tolerate the starting pulses, so may use a fill more tailored towards higher efficacy.

OK - understood, thanks.
I assume there's no visible spectrum change with Penning mixture lamps - only a lower efficacy. I've checked charts at Osram.com and they look identical. (But it's possible they have only one HPS spectrum chart for all the lamp category as there's the same spectrum chart even for a HPS Plantastar-T that should have its spectrum optimised for plant growing.)

There is difference in the color: The basic shape is indeed the same (it is still mainly a HPS after all), but there are some differences.

Osram NAV-E Plug-In starts red and the regular NAV-E starts white.
Also, NAV-E Plug-In have a longer hot restrike of 2 mins, because of a bi-metal that disconnects the starting electrode after warming up, so the lamp can't start until that electrodes connected again, NAV-E restrikes almost instantly.