If you don't intend to keep
SPS, clams, or anemones, I'd probably go with a 4 bulb
VHO system...440 watts total.
VHO isn't the best lighting available, but it really lends itself to a 4' tank because 110 watt bulbs are available in 48" and 46.5" lengths. You could do
PC's, but I think the
VHO would be easier to set up. One advantage to
VHO is that they use waterproof endcaps so corrosion usually isn't a problem as it can be with
PC's.
I should point out though, in most cases, we tend to want to keep
SPS eventually. If you went with a 2x250w
MH system, you could keep
SPS in the upper regions of the tank later if you wanted. The
VHO system will be sufficient for soft corals though. I would recommend an Icecap ballast as I've had very good service from them and they are repairable if they do quit.
