thanks for clarifying that 20, i should have said that instead of rollingeyes but these threads can be frustrating. there are two of these threads on this page right now.
8 or so years ago when i got into the saltwater part of this hobby i had PC lights. having had those lights is what responsible for me researching clams. the LFS would always say, sure you can keep that clam under those lights. but they kept dieing,LFS would say well they need iodine, or they need phyto and on and on. but the results were the same. so luckily i stopped listening to the LFS and looked for my own answers. just by looking at where these animals come from in the wild should tell you that they need very intense light. unfortunately PC lights are not the best choice for clams, sure some people have been successful but many more have failed.
when people say that its not a good idea, most of the time they are saying that from experience. there saying that for the health of the animal and to help try to insure your success, save you money and to keep you from needlessly killing an animal. its not a backhanded "your lights suck" comment but it seems that that's how most people take it, and then they go into "ill prove you wrong mode"