JFK

Metal halide bulbs/ballasts throw primarily blue light. Blue light is the most similar to early-mid day/spring sun and will be the best for promoting strong green growth in your bananas. Sodium bulbs throw almost all red/orange light and this replicates late day/fall sun and would be good for plants that flower or fruit. I wouldn't get a high pressure sodium setup as they encourage leggy growth and less than perfect leaf formation....they are really only good for flowering. The best of both is a metal halide bulb that has a mixed spectrum. Hortilux makes a really nice one. That is, a halide that is naturally high in blue spectrum, but with some added red spectrum. This is the closest thing to the natural sun and I've seen first hand how well they work.

For overwintering, you should go with a halide ballast/bulb and get a good bulb. So many people try to save money on the bulb, but this is really the best place to spend a little extra.

For seasonal/non-commercial use, I'd get a less expensive ballast, less expensive reflector and a really good bulb (the hortilux metal halide in wide spectrum won't disappoint-it was about $75 last time I got one and last multiple seasons).

Hope this helps.