I currently have a T5 Fluorescent Fixture which one socket broke. I got a great deal on LED Bulbs which are a direct replacement to T8 Fluorescent bulbs. Would I be able to reoutfit the fixture with T8 Sockets, or would I need to change the ballasts too?

2 Answers 2


The T5 fixtures have several differences the first is they are shorter than a T8 so no you can't use the T8 lamps.

2nd would be, The tombstones are smaller in a T5 and not compatible with T8 or T12.

Last the T5 fixtures and lamps I use require 54w ballasts where the T8 only require 30-40w this may be a problem for both the ballast and the new led lamp if you could make it fit.

A new fixture is the only real path forward for T8 but T5 tombstones are inexpensive if you want to save the fixture.

  • Typically an LED replacement for fluorescent is going to be no-ballast and directly wired to 110v, which means the reference to ballast power capacity isn't a factor. Certainly length differences would make it difficult for a swap.
    – fred_dot_u
    Commented Jul 20, 2017 at 23:26
  • Not true Fred_dot_u. There are more retrofits available that use the ballasts because of U.L. listing problems with 120v. If those that are out there many are single end powered because of U.L. I don't like those and won't use them. I have seen two many tombstones break, having 120 on each end makes sense to me but the mfg's that were shipping these for direct wire pulled them because of U.L. It makes no sense to me to use a ballast then transform the power again because some efficiency is lost but that is How the majority of retrofit LED lamps are designed.
    – Ed Beal
    Commented Jul 20, 2017 at 23:38
  • Thanks for the clarification. It's not unlikely that my area resources have limited their stock to the 110v versions only. Curiously, two of my purchases stretched over a period of time resulted in a one-end model and a two-end model, both 110v without ballast. Clearly no real standard to make life easier for DIYers.
    – fred_dot_u
    Commented Jul 20, 2017 at 23:44


T5 tubes are actually shorter than T12 tubes by about 2 inches.

In many native-built T5 fixtures, the fixture is built for that size, and that is that. You can tell these because it would be physically impossible to fit an actually-47-3/4” tube.

Some fixtures are actually engineered for T12/T8 and use T5 extension tombstones to close the 1" gap on each end. Those, you can just swap in T8/12 tombstones.

Other fixtures are notched in a way where they can fit either type of tombstone.

You will have to see what kind of fixture you do have.

Beware of "great deals"

Prices are dropping very rapidly and for instance I could get good Sylvania units for $6 each, last I checked.

These are all engineered products that take some careful match-up to work correctly, even if they can be made to fit. For instance, direct-wire tubes will work well enough by modifying the fixture. However plug-n-play tubes require the correct type of ballast. A T5 ballast may not be a usable voltage or current. Those made for instant-start ballasts will never work with a T5 ballast, as those are by definition rapid or programmed start

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