As far as lighting goes I'm using a coralife PC 65w X 2. I really took a gamble trying a clam with PC's, but so far so good. It seems to be doing great with tons of new growth.
You can do clams with PC if there is adequate PAR and intensity of light, as well as plenty of other factors required for their well-being. You could put a clam in a 125 gal tank with 400w halides...but if your husbandry skills and dedication are lacking, you're going to end up with a dead clam. Smaller tanks are generally harder, and keeping specimens like this tend to require some more finely-tuned husbandry.