A T8 fluorescent tube is 1" across and a T12 is 1-1/2", because the number is the width in eighths of an inch. Four-foot tubes of both sizes are 48" long on the same two-pin base, the medium bi-pin (G13).
The sizes in the code
| Code | Eighths | Across |
|---|---|---|
| T5 | 5/8 | 5/8" |
| T8 | 8/8 | 1" |
| T12 | 12/8 | 1-1/2" |
The length isn’t in the code. Tubes come in lengths such as 2 ft. and 4 ft.
Watts and light
| Tube | Type | Watts | Lumens |
|---|---|---|---|
| Feit F40DX/2 | T12 | 40 | 2,325 |
| Philips F40T12/CWSupreme/ALTO | T12 | 40 | 2,600 |
| Feit F32T8/941/2 | T8 | 32 | 2,600 |
| Feit T1248/4CCT/LED/2 | LED for T12 | 20 | 1,800 |
| Feit T48/840/LED/2 | LED for T8 or T12 | 14 | 1,750 |
From Feit’s product pages and Philips’ 2015 lamp guide (initial lumens). Color and brand change the numbers, so compare the box of the tube you’re replacing.
Feit’s 32 watt F32T8/941/2 is rated for the same 2,600 lumens as Philips’ 40 watt F40T12/CWSupreme. Feit sells its F40DX/2 as a replacement for F40T12 tubes, and its F32T8/941/2 for F32T8s.
Swapping one for the other
The pins and the length match, but a fluorescent tube runs on the ballast inside the fixture, which controls the current to the tube. Use the tube type the fixture’s label names. The ballast’s own label is inside the fixture cover, with the wiring, so have an electrician read it. Changing a ballast means rewiring the fixture, so leave that to an electrician.
LED tubes
- Type A, plug and play, works with the fixture’s existing ballast if the ballast is on the tube maker’s compatibility list. Feit sells its T48/840/LED/2 as a Type A tube for T8 or T12 fixtures.
- Type B, ballast bypass, needs the ballast taken out and power wired straight to the sockets. Have an electrician do that. The linear LED tubes in Westinghouse’s catalog, made for T8 and T12 fixtures, are this kind.
- Type AB works either way, on a compatible ballast now or wired direct later. See T8 LED tubes for the ballast checks.
To check a ballast against Feit’s list, you need the model number printed on the ballast’s label.
Turn the power off before you take a tube out. Feit’s steps rotate the tube 90 degrees, then pull it down out of the sockets.
Another shape?
Bases and shapes