How to Replace T12 Lamps With T8 Lamps

by Joe McElroy; Updated September 26, 2017
New T8 fluorescent lights are thinner and more energy efficient than the old T12 types they replace.

Replacing T12 fluorescent lamps with T8 lamps saves energy, eliminates buzz and increases light efficiency by 12 to 30 percent. Best of all, it is an easy replacement because T8 ballasts and lights can be installed on existing T12 fixtures. The T series of lights are fluorescent light tubes, usually used in commercial settings. The "T" indicates that it is a tube and the number that follows gives the diameter of the tube measured in eighths of an inch. Thus a T12 is a 1-1/2-inch-wide tube while a T8 is an inch-wide tube.

Items you will need

  • T8 ballasts
  • T8 lamps
  • Safety gloves
  • Wire snips
  • Socket set
  • Twist wire nuts
Step 1

Turn off the power to the fixture you will work on at the junction box before you begin. Wear electrical safety gloves throughout the replacement process.

Step 2

Remove the cover from the fixture, if it is equipped with a cover; then, remove the T12 lamps from the ballasts at each end of the tubes.

Step 3

Cut the wires to the old ballasts several inches from the end using the wire snips. There are two wires to each ballast.

Step 4

Use the socket set to unscrew the nut that mounts the ballast to the fixture while holding on to the ballast with your free hand. There will be either one or two mounting nuts on each ballast. Remove the old ballast and set it aside.

Step 5

Mount the new ballasts into the fixtures and secure them with mounting nuts.

Step 6

Strip 1/2-inch of cover off of each wire. Connect the matching colored wires to the the new ballasts with the twist wire nuts. Make sure to fully secure the wires so that no metal is exposed.

Step 7

Insert the T8 lamps into the new ballasts, replace any cover over the fixture and turn the power back on.


  • It is an easy fix to replace the ballasts on existing fixtures, but you can increase energy savings by installing entirely new fixtures specially designed for T8 systems.

About the Author

Joe McElroy has been writing on politics and culture since 1983. His articles have appeared in a diverse array of publications, including the "Chicago Daily Observer" and "Immaculata" magazine. McElroy works occasionally as a strategic consultant to federal candidates. He majored in American history at Northwestern University.

Photo Credits

  • Ryan McVay/Photodisc/Getty Images