Can a 175w Metal Halide lamp (the regular probe start type, NOT THE PULSE START LAMPS), be lit/run on a 175w ballast for Mercury Vapor lamps?

Probably not, at least not without an ignitor, and even if they would ignite, the lamp may not last as long.  The MH ballasts have a higher OCV and a lower current crest factor.  It does work the other way around, though.  Most MH ballasts listed the ANSI ballast specification for the same wattage MV lamp until they banned MV ballasts here. My 400W MH ballast lists M59 (400W MH) and H39 (400W MV) ANSI codes and runs both types of lamps just fine.

 it might have a hard time striking or have a stable arc on mercury H39 ballast
 but not reverse like metal halide probe start ballast due to OCV and current but   will run. it slightly defferent than mercury ballast. from what i heard.

If I understand correctly, it is always best to run a MV lamp on a MV-only ballast instead of an equivalent MH ballast ?

@ sol however the probe start metal halide is dual listed for metal halide or MV
but when the MV ballast ban went in effect they delist the mercury vapor from the label.
i do agree mv lamp perform better on mercury ballast. those metal halide ballast do run a bit hotter than mercury ballast this is do to cheaper aluminum winding they used on some of them.

The problems with MV ballasts running probeMH is the starting and the production tolerance of the lamp current (MH asked for tighter spread then was sufficient for MV).

MH ballasts are either heavier, or have higher losses. That is, because the higher OCV need more turns, what mean longer and thinner secondary wire have to be used in order to fit into the same space. Consequence is higher wire resistance causing the losses.
Other aspect is the need to use higher voltage rated capacitor.

But from the lamp "point of view", there is no ill effect at all, the MH ballast fulfill all electrical requirements the MV lamp have for the ballast outpu. The MV delisting is exclusively due to the MV ban

I wonder if this is true of 240v ballasts? However we don't have a 175w equivalent here as far as I know. Apparently a 40w merc can be run on a 35w MH ballast but how close an electrical match would this be? I only currently have 1 40w clear MV bulb and wouldn't wish to stress it.


BG

Just to clear this up, yes you can run a 175 watt MV on a MH ballast without any problems, in fact I bought 175 watt MH ballast last year and it was rated for 175 watt MH, 175 watt MV and 150 watt MH.

On 240V 50HZ the power ratings of MH and mercury are different in the low power ratings :

Merc - 50 80 125 250 400

Pulse start MH / HPS - 70 100 150 250 400



The ballast for the _Pulse Start_ 400 MH and 400 merc is the same - i have one. Dont know about the 250W

The Pulse Start MH and HPS use the same ballasts at least in the lower wattages

I remember 175W MV's here (230V area). They are compatible with 150W HPS ballast (without ignitor; 230/240V area).

The probe MH need higher voltage for striking, but otherwise is compatible with 175W MV.
Therefore the US 175W MH ballasts were designed to use higher OCV (~300V) then 175W MV ballasts (~220V). This mean the MH ballast could be rated to run the MV lamp (technically, not legally for new ballasts, as sale of newly made/imported ballasts for MV are banned in the US). So the ballast "175W MH/MV" is the one with higher OCV

But in the opposite (running MH on MV-only rated ballast) may cause ignition troubles, mainly at cold, the 220V is insufficient as OCV for probe MH.

Other problem is the ballast current accuracy: MH's require tighter arc current tolerance to maintain the rated color, what meant MH ballasts were made with tighter tolerance. This is, of course, not any problem for MV.
But less accurate MV ballasts may run each lamp in an installation at slightly different power, what cause disturbing color variations with MH's