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What are T5, T8, and T12 Fluorescent Bulbs?

  T5, T8, and T12 are different models of the fluorescent light tubes typically seen in office buildings and classrooms. The “T” stands for “tubular.” The number following the T indicates diameter size in eighths of an inch. In other words, a T5 fluorescent lamp is a tube with a diameter of ⅝ of an inch. A T8 tube is 8/8 of an inch, or 1 inch.

Which Fluorescent Light is Best for Growing: T5, T8, or T12?

  Indoor growers who choose to use fluorescent tubes as grow lights prefer T5 lamps. Compared to the other fluorescent options, T5 tubes are more efficient and available in a range of color temperatures.