You are going to want to get a heat sink if you are running 42 LEDs. It is an extra cost but compared to having the x dollars of 42 leds burning up prematurely would cost a lot as well. I am designing a set up for my new reef tank and just building it in strips. This way you can expand as you need more light and the narrower heat sinks are much cheaper. you could also find a computer recycle place and get a bunch of smaller heat sinks from computers and install them in a line on some aluminum channel.