Ocular Holo Matrix (OHM) Optics: Meridian OHM Optics are simple to swap and have 3 models, each suited to meet the needs of different aquarium styles. Balance: This is the default lens included with the Meridians. It is designed to suit aquariums from 18-36" (45-90cm) top to bottom. Focus: Focus lenses provide a more concentrated light for aquariums over 36" (90cm) top to bottom. Encompass: Wider spread designed for shallow tanks under 18" (45cm) top to bottom. Ideal for frag tanks, or covering a larger area for lower light corals in deeper tanks.