At the lfs i work at we keep our clams under halides until they are sold. However, i know many of our customers have had success keeping them under PC and VHO lighting, in fact the owner has a 300 gal reef with only PC lighting, all 5 of his clams and the many corals look great. He does have a lot of watts of PC though, so if you have over 5 watts a gallon that sould be enough
Temperature seems to be one of the most important factors as well as water quality so if you can keep the temp stable and the water good you should do okay.
I have kept a growing deresa quite successfully under power compacts for over a year. I evetually put it in a tank with halides though, so I can't comment on long term success, but it grew nicely while under the PC's, and I had every indication that it was happy and healthy.
I would also dose phytoplankton from time to time.
I'm hoping to keep a Derasa under MH (220 watts over a 30x18x18, 40 gallon). I've done a fair amount of research, and just about everything I've read indicates that PC or VHO is sufficient as long as it's not an especially deep tank.
