Electronic ballasts are more efficient than magnetic ones. They use less power, generate less heat, and are quieter. They are also more expensive up front.
No. The lamp has to match the ballast. The lamp will not ignite if the wrong ballast is used.
Yes assuming the ballast is also for a metal halide lamp.
a compact electronic ballast in the base of the lamp
No, the ballast has to be matched to the lamp. 250 watt ballast, 250 watt lamp. Also be sure to match the lamp type to the proper ballast even though the wattage is the same. HPS ballast to HPS lamp, Metal halide ballast to metal halide lamp and mercury vapour lamp to mercury vapour ballast.
No. The bulb has to match the ballast wattage exactly. And you can't interchange different lamps (like metal halide) either. The ballast is specific to that wattage and lamp type. The bulb will either burn out quickly or just not work properly at all
yes
yes
To answer this question the voltage of the ballast must be stated and the type of lamp in the fixture.
Not recommended. It would work but shorten lamp life and may cause risk of fire. However, if you just wanted to check a lamp was capable of striking it would be ok for a few minutes. I've done the opposite in the past and used a 150w lamp with a 100w ballast. Works, but not good for any of the components, including lamp.
No you can't. You can use a metal halide lamp of the exact wattage of the original mercury lamp. You cannot vary on wattage at all.
Yes a ballast uses amperage. That is the number beside the letter A on the ballasts nameplate. Depending on the size of the lamp or lamps will govern the size of the amperage that the ballast will draw.
No. A mercury vapor lamp will work on a metal halide ballast, but not the other way around.