I'm currently working out a design for a shelving system for growing seedlings and mature plants indoors. I'm going to hang lights from the bottoms of the shelves to illuminate plants below...I've already figured out I can use shop lights for the seedling shelves (I figure 4 T8's should provide plenty of light for a shelf measuring 48" x 18"), but I was wondering if it would be worth my while to invest in a HID light for growing mature plants on another shelf. If so, what's an ideal output for an area of 6 square feet, and what distance from the plants should the light be positioned? If the shelving system is in an open space, will I still need to invest in an inline fan for the HID light fixture? I've looked for answers, but couldn't find anything too definitive. I apologize if I've overlooked relevant information.