That isn't really a fair question, because all 384w aren't over the clam. If your tank is 4' long, than you really have 192w of light over where the clam is, and what needs to be considered is how tall the tank is due to how light levels (PAR) decrease for every inch it has to penetrate.
Derasa clams are usually something that will do well under VHO and PC lighting, because they aren't too light demanding.
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