T5’s, T8’s, T12’s, also known as “linear fluorescents”, are all the long, tube shaped bulbs that we are all familiar with. The bigger the number after the “T” the bigger the bulb. T12’s are the typical “shop light” bulbs and T8’s are what the lighting in most commercial buildings are being converted over to because they are more energy efficient. T5’s are the current standard in grow lighting because they are so thin that you can fit up to four of them per foot of width in a fixture, offering tremendous light intensity.
Compact Fluorescents, or CFLs, pack a maximum amount of T5 grow light tubing into a small space by winding and bending the tube. Lower wattage CFL grow lights, such as 26 and 32 watt, can be used with standard household lighting fixtures, while higher wattage CFLs, such as 125 and 200 watt, require specialized fixtures similar to HID reflectors, but with the ballast included in the hood.