It is a classification of the fluorescent tube lamps.The letter T is used to indicate that the focus fluorescent is of type tube. The number that follows indicates the diameter of the pipe measured in fractions of an inch (1 inch = 2.5 cm). The diameter of the tubes is measured in eighth of inch. For example, a tube T5 has a diameter of 5 / 8 of inch, the T8 has a diameter of 8 / 8 of inch, i.e., 1 inch.
