Here is an info on magnetic ballast..that will run MH bulbs

250w bulbs

Probe start: ANSI: M58, core, capacitor
Pulse start: ANSI: M138, core, capacitor, ignitor
HQI: ANSI: M80, core, capacitor, ignitor
EYE: ANSI: H37, core, capacitor, actually a mercury vapor ballast
Electronic: ANSI: none, metal box with wires

Probe start will run american bulbs with ignitors built into the bulbs like coralife and venture bulbs. some german and euro bulbs will run fine on these, but without an ignitor, the bulb struggles to light and bulb life may be decreased. also reliabilty goes down.

Pulse start will run the german/euro bulbs (ushio, AB, radium, etc.) these bulbs don't have built in ignitors, so the ballast has the ignitor wired into the circuit. the ignitor provides the high voltages needed to fire the bulb. you can run probe start bulbs on these ballasts, but the two ignitors may try to fight each other and possibly cause a fire.

HQI ballasts are similar to pulse starts in their wiring and ability to run bulbs. the output is a little higher which is meant to run the double-ended bulbs (commonly called HQI bulbs). people run mogul bulbs on these and they run a little hotter and brighter because they are being overdriven. this in turn shortens the life of the bulbs.

EYE ballasts are mercury vapor ballasts. they are similar to a probe start ballast, but the only bulb you can run on these are Iwasaki 6500K bulbs (because these are actually MV bulbs, not MH bulbs like most think). the ballast will damage MH bulbs if you try to run one on it.

Electronic. these will run any bulb at the rated wattage: probe start, pulse start, iwasakis, DE (double ended-HQI). if you think you might change your mind in the future, get an electronic. you can change bulbs to whatever you want and not have to worry about the ballast being the wrong type. electronics run cooler (a magnetic MH ballast will burn your hand if you touch the coil after it's been running for awhile). they also use less energy.

Additional info:

175watt:
Probe start: ANSI: M57, core, capacitor
Pulse start: ANSI: M137, core, capacitor, ignitor
Electronic: ANSI: none, metal box with wires

400watt:
Probe start: ANSI: M59, core, capacitor
Pulse start: ANSI: M135, core, capacitor, ignitor
HQI: ANSI: SON AGRO, core, capacitor, ignitor (this is actually a 430w HPS ballast used primarily in hydroponics)
EYE: ANSI: H33, core, capacitor, actually a mercury vapor ballast
Electronic: ANSI: none, metal box with wires