The T5 bulbs come in 1 bulb, 2 bulbs, 4 bulbs and 8 bulbs. The also come in both 2' and 4' lengths. I have several of the 1 bulb fixtures to go with my larger fixtures. They allow you to move around the lights giving great flexibility. I use 3 single bulb fixtures over my moms and use a 4 bulb fixture plus a couple 1 bulb fixtures for my vegging plants. I also use them for rooting cuttings. I use 2 single bulb fixtures about 2 ft. above 50 18oz containers--around 3000FC.