I did a fairly extensive set of testing with overdriven lights using WH7's as I overdrove lighting my self. I can say that an overdriven NO has nowhere near the intensity of a 175 watt MH, for that matter an overdriven NO isn't even half the intensity of a PC of the same length. If you do a search on overdriving on this board you will find my old tests.
I still overdrive NO actinics to VHO levels but the VHO still has a higher PAR output than the NO running at VHO power levels (mopre than twice the PAR value)
Two MH on the tank will make it a lot brighter than overdriven NO bulbs but it will also give you more contrast between the shadows and the light (looks kinda neat to me) a flourescent will give your tank a flat lighting look with less definition between the light and dark.
I used to have 4 overdriven NO's on my tank and one 175 watt MH, when the MH came on it outpowered the NO's so bad you couldn't even tell they were on except for the lighter shadowed areas.
I went to the MH because the SPS didn't grow or color up under the overdriven lights and with the 175 they were alright but I really noticed a difference with the 250 watt bulbs on a hqi ballast.
Steve
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 *everything said above is just my opinion, and may or may not reflect the views of this BBS, its Operators, and its Members. If cornered on any “opinion” I post I will totally deny having ever said this in a Court of Law…Unless I am the right one*
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