What is T5, T8 and T12 lighting?

Written by karl martin
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What is T5, T8 and T12 lighting?
Inexpensive fluorescent lighting is ideally suited for commercial use. (neon light image by Eldin Muratovic from Fotolia.com)

Compared with incandescent lights, fluorescent bulbs are relatively inexpensive, longer lasting and use less energy. For these reasons, fluorescent tubes are used in industrial, commercial and public facilities. The most common straight tube types are T5, T8 and T12, available in lengths up to eight feet. All fluorescent bulbs require a ballast to operate, while older models require a starter as well.


The letter T is used in front of the number to show the fluorescent bulb is a tube type. Following the letter is a number representing the diameter of the bulb measured in fractions of an inch. Fluorescent bulb widths are measured in eighths of an inch. For example, a T5 bulb is five-eighths of an inch wide, a T8 bulb is 1 inch wide (eight-eighths) and a T12 is 1-1/2 inches (12/8ths) in diameter.

T12 Type

Since its invention in the 1930s, fluorescent T12 bulbs were the choice of building contractors. The low cost and lifespan of 20,000 hours far surpassed incandescent bulbs. However, because of its less efficient magnetic ballast and larger inefficient bulb size, it has lost popularity to the T8 electronic ballast type. T12 and T8 bulbs are available in the same lengths, however, ordinary T12 bulbs do not operate properly with an electronic ballast and vice versa. According to the National Lighting Board (NLB), a ban effective July 1, 2010, phases out magnetic ballasts, although excess inventory and T12 bulbs will continue to be sold.

T8 Type

Fluorescent T8 bulbs have continued growing in popularity since their introduction to the United States in 1981 and have now become the standard in building construction. The T8 bulb's lifetime meets or exceeds that of the T12, while using less energy. Additionally, the T8 uses an electronic ballast that is more energy efficient than the T12 magnetic type. With the T8 ballast using solid-state circuitry to operate, it does not make a loud humming sound or cause light flickering commonly found with the T12 magnetic ballast.

T5 Type

The T5 fluorescent bulb, like the T8, uses an electronic ballast. That is where the similarity ends. The cost of T5 bulbs, especially high output types, is significantly higher than T8 and T12 bulbs. T5 bulbs are also shorter and do not fit standard fixtures. For example, a typical T5 bulb is 46 inches long rather than the 48 inches (4 foot) of T8 and T12 bulbs. Conversion kits are available, with a ballast, allowing T5 bulbs to fit T8 and T12 fixtures. T5 bulbs save money over time because of a longer lifespan while producing more light with less wattage. The T5 also maintains maximum light output for almost the entire lifetime of the bulb.

Future Technology

T5, T8 and T12 LED (light emitting diode) replacement tubes currently on the market fit into existing fluorescent fixtures. The technology of LEDs is different from fluorescent bulbs with advantages and disadvantages. The biggest factor is price, easily costing ten times more. The advantages are they last up to 50,000 hours, use less power, operate without a ballast and do not contain hazardous mercury that fluorescent bulbs use. Like any new product, cost reduction will depend on improved technology and consumer demand.

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