Most will tell you that you will want to get metal halides. The clams that will do with less light, also tend to grow larger...certainly much larger than a 55 will handle...in a 55, you are most likely going to be looking at croceas since they stay around 6"...and croceas need good lighting. You can can get mh lighting for a 55 for a fairly reasonably price. I got two 175 watt ballasts for my 55....about $100 each....then figure another $50 probably for the sockets and reflectors....about $30 for fans....and the price of the bulbs....anywhere from $30-100 a piece.