Difference Between T8 & T12 Lamps

The T8 lamp has supplanted the T12 as the standard for fluorescent lighting fixtures. Lamps are the fluorescent equivalent of incandescent light bulbs. Does this Spark an idea?

Tube Diameter

The “T” number is the diameter of the lamp, measured in eighths of an inch. So a T8 lamp is 1 inch in diameter, while a T12 lamp is 1.5 inches.


The narrower a fluorescent lamp, the more energy efficient it is. Replacing T12 lamp systems with T8 systems can produce energy savings of up to 40 percent, according to lamp manufacturer Universal Lighting Technologies.


The difference in light output between T8 and T12 lamps of equal size and comparable wattage is all but indistinguishable to the eye. However, the T8 uses less power to produce light.


T8 lamps and ballasts–the transformer that moderates the current to the lamp–are designed to fit in the same fixtures as those for T12s.


As of early 2010, there was little cost difference between the two types of lamps, but that will change as manufacturers phase out T12 technology. The National Lighting Bureau, a consortium of manufacturers, considers the technology outdated.

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