Personanly I wouldn't keep clams under anything less than Metal Halide, But you can get by with VHO and PC if they are placed higher in the tank

BTW those Clams are/were Crocea's.

Ive done a little research and Ive come to the conclusion that clams are just not going to work for me. A Derassa, out of all clams may survive for a bit, but in order for it to thrive and be around for years I think it and all clams need metal halides.JMO

Both mine are under NO lighting and so far so good. The small one has 7 new growth rings visable in about 9 months. The large one I've only had for 6 weeks so far.
Pictures are very poor but will have to do until I can afford something better than a $200 Cnd Kodack.
CLAM PAGE

I did not have great success with my only Crocea under 200W of PC lighting. While I thought it was doing well and stopped feeding DT's because of that, it eventually died one day after no prior warning. I assumed it was from lack of light. Had I continued to feed DT's, it is not certain if it would have helped extend its life. It survived for 2 months only.

However, I have a Derasa that did OK under PC lighting. It was under 110W of PC lighting for 6 months before I upgraded my lighting.

Nice Croceas you got Ray. Wow, 9 months under NO. Pretty good.