The dome should fit as close to the top of the cutting as possible allowing for different heights of course, then your flourescent light as close to the top of the dome as possible. The one I show in my pics is available at any grow shop and runs around 3 bucks for the dome, another 3-4 for the black plastic tray the dome fits fairly snugly on. The clone kit comes with another tray that fits inside the main tray that will hold up to 64 cuttings in recessed holes made for rooting/seed pellets with a small reservoir in the bottom for watering pellets through the wick process. They also come with a heating pad and the clear plastic dome.