Came into some T12 bulbs, but the fixtures we have are T8.

Any issue with using T12 bulbs in T8 fixtures?

They should not work, but sometimes do. Also T8 sockets are generally shorter so the lamps may not work. The lamps are pretty much useless nowadays.

The pins seem the same & they're both 48" bulbs.
The T12 are just a larger diameter.

They are the same length, and will work. However once I installed some T8's into a custom lighting cabinet that had T12's.

The ballast overheated and almost caused a fire.

Not a good idea

Still a number of T12 fixtures around. If I were local to you, I would offer to buy new T8 and trade you for some T12 lamps. Maybe someone there needs them and would make you an offer.

I believe the answer depends on your ballast. Some have a wider range of applicable bulbs than others.

When I was still doing electrical at work, we could never get the custodial stuff to understand that there were right and wrong bulbs, and just because it fit didn't make it right. I actually started writing inside the lights with magic marker... "bombilla flaco" and "bomilla gordo" but even that didn't help. When correcting one woman I was told.. "No, I like these ones better." lmao

Anyway.. I seem to recall the life of the bulbs being shorter, but I can't recall which way (T8s in 12 fixtures or vice versa) was worse. Over driving them or under driving them. I don't recall changing any more ballast that normal, we certainly had no fires and we had thousands of ballasts.

I have found T12 in a T8 fixture. And vice versa. Both working fine.

I have also found one T12 and one T8 in the same 2 lamp fixture. There are real stupid lamp changers out there.

At my gun club we have switched a few T12 LB240 over to one end LED direct wired. I fear those stupid lamp changers more now.

I don't know how many bulbs you have but LED's have become really cheap if you buy them 25 at a time online. You can get the type that don't use a ballast and they pay for themselves in 6 months or less in energy savings. You use T8 or T 12 fixtures.
My shop where they run about 8 hours a day was a 3 month payoff with better, brighter light.

Well, got lucky. Pulled the cover off the fixture in our laundry room & it had 2 T12 in it.
One had burned out, so swapped in one of the new ones.

Master closet & garage are all T8.
The LED T8 we got say electronic ballast only, would that be marked on the ballast?

If you buy LED's, get the ones for no ballast. The wiring is really simple and you remove the ballast (a potential fire issue) and a cause of failure later.
The savings in energy is substantial.

quote:

Originally posted by P250UA5:
Well, got lucky. Pulled the cover off the fixture in our laundry room & it had 2 T12 in it.
One had burned out, so swapped in one of the new ones.

Master closet & garage are all T8.
The LED T8 we got say electronic ballast only, would that be marked on the ballast?

98% or greater of T8 are electronic, I've only seen a handful of magnetic T8 ever, and I've seen thousands of fixtures. You would have take the cover off to tell. Magnetic ones are about 3" wide, electronic are half as wide, and will likely say electronic on the ballast.

Update on this
Put the LED T8s in 2 of the garage fixtures (4 bulbs)

Dramatic improvement in lighting, especially from the dim fluorescents that were in there.

1 of the fixtures lights the LEDs pretty dimly, but a off/on of the switch pops it to full brightness. This happens about 1 in 10 times.