for a FOWLR, you dont need great lighting... just what looks good to you.. fish dont use photosynthesis to gather energy, just plants and corals.
the life on rock will stay live without light at all... only thing which you will notice is that any coralline algae (the reds, pinks, purple colors) will bleach out since they require some decent lighting.
PC and VHO are fairly similar. both are variations of florescent lighting with much higher watts of power... for example, a VHO and a regular florescent look very similar in size.. for the 4 foot length models, regular florescent are 40 watts, compared to VHO which are 110 watts.... PC lights are "compact fluorescent" with alot of Power, hence the name.. Power Compact Fluorescent, or PC for short... (VHO is Very High Output)
MH (Metal Halide) are basically incandescent lights on steroids. ranging from 175, 250, 400, and the almighty 1000 watters. i dont think they make em stronger.... these lights require their own cooling systems (a fan just for the lights) because of how hot they run compared to the fluorescents mentioned above.
Lighting for fish tanks are more expensive for one simple reason... its more expensive to produce a full spectrum (like the sun) than it is with regular lighting... you can actually get MH and PC without the full spectrum, which would cost much less... the lighting for your home doesnt really contain much of the blue specturm whereas most tank lights contain the blue spectrum which is more natural for the livestock which require lighting.
The spectrum on tank lights, although contain the full spectrum, also are measured by the strength of a certain spectrum. For example, MH come in 6700k, 10,000k and 20,000k (among others, but these are most common).. it goes from red, to white, to blue respectively.
For your situation, if you already have lighting, and you dont mind how the tank looks, dont do anything yet..... wait several months and do some research till you figure out what you want to keep in your tank down the road... .you may find yourself saving alot of money by purchasing lighting once instead of constantly upgrading your lighting.
Another note, is the algae growth... "bad" lighting (either old bulbs or regular lighting) may promote algae growth... and you will have to figure out a way to minimize the other qualities that the unwanted algae require... such as using RODI water.....
hope that helps.
