My opinion is, and I"m probably wrong, is that they are both fluorescent bulbs and basically the same when it comes to results. While they have some minor differences they have similar characteristics and limitations when it comes to the sea creatures and what they get out of it. IMO to really break out you need to go to metal halides. I tried PC and VHO and did not see a difference between the two. When I took the plunge and bought some MHs I noticed a difference immediately. Simply put, there is no replacement or substitute for MHs. I will only use PCs or the like to augment my MHs. Thats just me....