T5 lamps offer very high output from a fluorescent tube, they do require a special ballast unit to run, but can have many applications especially in smaller aquariums or where you want to keep the lid on. The Aqua-Medic range of replacement T5 lamps which offer very good value for money (especially when bought in the 4 pack), for use with any manufacturers ballast unit, available in marine white, blue and freshwater white (for plant growth)