It is possible to grow them under normal daylight FL tubes but you must have enough of them to reach high intensities and your clam must be only a few cm away from them. I would say at least 4-5 FL tubes over a clam. But then again...normal FL are quite wide in diameter and having so many can be a waste of electricity as only the ones directly above the clam provide the most light. It is best to invest in lighting like MH or at least T5s that can provide higher light intensities (as they are higher in PAR and you can fit more over a clam) directly over the clam..