Just to make this clear for anyone new to clams or not sure about lighting requirements, it's virtually impossible for you to provide too much light for clams in our tanks. It's true that there can be light shock in some cases where the clam has been kept in poor/subpar lighting for too long, but you can easily raise the lighting in a matter of a few days and the clam will adapt. My general rule for crocea, maxima and noae is, 350+ micro moles (if not more) for at least 8hrs of full spectrum daylight. Squamosa, derasa, gigas and hippopus should get 250+ micro moles for the same duration. The bigger clams can adapt to lower light, but only if they are putting on new shell growth, which is the biggest indicator for a healthy clam. If it's not putting on new shell growth, it needs more light. It's that simple. All species that we keep in aquariums are found in very shallow water, with the intensity reaching 2000+ micro moles during that time. As
@OrionN mentioned, these clams are completely exposed during low tide and those numbers go even higher. The larger clams are also found in deeper water, but not as deep as you think.
If you're considering getting a clam, make sure you have the room for it and that you can provide enough light for the clam (and that the surrounding corals will be fine or thrive in those conditions). I can't emphasize it enough, but people need to do research before buying these (and other) animals before putting them in their tanks. If you're going to spend the money on these animals and not do research for their care, then you're just wasting your money and their lives. We need to take some personal responsibility here and make a concerted effort in learning about their (and other reef creature's care) care requirements before bringing them home to our little slice of the reef. Apologies (not really) for sounding a little militant, but clams have a special place in my heart and I want hobbyist to be successful keeping them. My first piece of advice is always, buy James Fatherree's new book on clams before you buy a clam or want to learn more about their care. $36 is nothing compared to the wasted money on a beautiful clam that's only going to live a short life because you (the hobbyist) didn't want to do the research required for their care. Okay, I'll step off my soapbox for now. Happy reefing and I hope everyone can experience these beautiful animals, they're simply amazing.