Metal Halide question

[swill]

Can you use a 400W ballast with a 250W bulb?

[gobytron]

no.

You'll over power the bulb (if it even lights up) and you'll risk fire, over heating or possibly a blown bulb.

[SeaHorse_Fanatic]

Yup, unless its an adjustable wattage ballast, you need to match bulb to ballast.