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I would like to add a few things:
The HQI (ANSI M80) will overdrive most North American lamps but not all single-ended lamps. The Radium 250-watt blue lamp is one that is designed for this ballast.
The M80 is best suited for European double-ended and most single-ended lamps.
The Pulse Start 250 (ANSI M138 / M153) will underdrive most European lamps. I personally don't see a good reason why this ballast is offered for the aquarium market. Currently there is no lamp that will operate properly on this ballast for aquarium use.
The pulse start 400 underdrives almost every European lamp (except the Radium blue lamp) but uses the correct starting method/voltage.
Currently the best ballast for Euro 400watt lamps is a true European ballast. The problem with this is the input voltage (only available in 220/230/240V) but this shouldn't be a problem for too long. A few lighting companies are working on 120V Euro type ballasts that won't need a step-up transformer.
I've spoken to a few people about the AB lamps in Europe (even the lamp manufacturer). These lamps are designed to be able to start at lower starting voltages than most European lamps. These lamps are equipped with a starting circuit (bi-metal switch and resistor) connected to an addition electrode (starting electrode).
The lamp chemistry causes the 175 and 250 watt lamps to have warm-up problems with standard probe start North American ballasts (Constant Wattage Autotransformer - CWA Type). These lamps require more voltage and amperage during warm-up than some standard ballasts can provide. With a standard ballast the arc becomes too thin and causes it to become unstable. Then the arc fails and starts again. Sodium usually prevents the arc from getting too thin but adding more sodium also changes the lamps performance in other ways.
The AB lamps will operate optimally on European ballasts. You'll get the best light color using a European or similar ballast (like M137/M152 for the 175W lamp and M80 for the 250W lamp).
Electronic ballasts are great for the lamps they are designed for.
An electronic 250W MH ballast will operate any 250W MH lamp like a 250W pulse start will. The reason is because both use a high Open Circuit Voltage (OCV) to start up a 250-watt lamp.
Currently more info is needed to know which lamp will operate optimally on what brand or model ballast. Personally I would like to see some testing done with 250 and 400 watt electronic MH ballasts. Currently I only have equipment to test electromagnetic ballasts properly.
It is very difficult to manufacture a 250 and 400 watt electronic ballast that will operate every 250/400 MH lamp optimally. This is because with 250/400 watt lamps you have 3 different kinds and each has different operating requirements.
Hope that helps
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