We typically recommend one module per foot on tanks deeper than 30 inches. On tanks less than 30 inches, one module every 18 to 24 inches is acceptable. Our latest generation System is significantly more powerful and produces greater spread than previous generations. Some users may be able to use fewer units depending on what type of corals they are keeping in their tank and how much light is needed. There is no ‘one size fits all’ answer to this question. What’s great about the AI System is that due to its modular design is that you can always you can add another module if you desire more light.