There is a distinct difference between metal halide, vho, NO, and pc. I'll leave the mh alone because I don't use those. VHO, PC, and NO lighting are types flourescent lighting. First, NO indicates normal output, VHO indicates very high output, and pc indicates power compacts. NO and VHO bulbs are very similar in the way they look. However, a 24" NO bulb puts out 20 watts, while a 24" vho bulb puts out 75 watts. The type of light emitted is different also. VHO being better in quantity as well as quality of light emited. Power Compacts are powerful flourescent bulbs that are compact in size. Each one of these has different characteristics in terms of output of lumens, depth of effective light penetration, asthetic look of the lighting, etc. It is up to you to research and determine what you want. I recommend choosing a lighting system based on what you want to keep both now and in the future. It will not do you any good to purchase for example, several normal output bulbs for your tank if you want to keep higher light requiring corals in the future. Good luck!