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Fluorescent Tube Diameters

T12 - 1 ½” Diameter, older type, not as efficient as T8 and T5. As a bulb gets older, the brightness will decline. Do not buy a new fixture with this type of bulb, instead buy one with a T8 or T5.  If the ballast needs to be replaced, either replace with a T8 ballast or purchase a new fixture (the price may be about the same).

T8 - 1” Diameter, a very common size fluorescent tube found in kitchens, garages, and offices. T8s with the newer electron ic ballasts use about 20 - 30% less energy than a T12.

T5 - 5/8” Diameter, is a smaller diameter. T5s with electronic ballasts use about 45% less energy than a T12.

How to Replace Fluorescent Tubes

A fluorescent tube should always be replaced with the same diameter bulb unless the ballast is changed to a different type. The lamp holders are made of plastic, so be careful not to break them when replacing these bulbs. Turn off the light switch before replacing bulbs. If you have difficulty gripping the bulb, use rubber gloves.

To remove the bulb, gently rotate 1/4 turn in either direction. If they don’t turn easily, reverse the direction of rotation to see if it turns more easily. Increase pressure while rotating bulb until it is removed.

Insert a new bulb into the lamp holders. Make sure the bulb is all the way into the lamp holders and gently rotate 1/4 turn in either direction (bulbs usually have alignment marks to indicate proper rotation).

T12 Fluorescent Tubes Discontinued

T12 fluorescent tubes are not made anymore because of poor energy efficiency. While these lamps are still in stock in some stores, replacing the ballast with a more efficient T8 electronic ballast could be a better choice.

U-shaped Tube Circline (circular) Tube T5, T8, T12 Tubes




Circline (circular)

Fluorescent Tubes are different than compact fluorescents because they are powered by a separate ballast to start up and operate the bulb. They have two common shapes, straight and u-shaped. The most common diameters are T12, T8, and T5. The T stands for tubular and the number indicates the diameter in 1/8 of an inch. Tube diameter is determined by ballast type. A fixture with a T12 ballast must use a T12 bulb. A fixture with a T8 ballast must use a T8 bulb, etc.

Color temperature range is 2700K to 6500K. Fluorescent tubes will reach full brightness right away, however a newly installed bulb will take a while to reach full brightness, especially when it is cold.


Fluorescent Tubes

Fluorescent Tubes TableFluorescent Tube Diameters Table

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