T12 bulbs are being discontinued and were actually phased out back in 2012.
The U.S. Department of Energy mandated that the production of T12 fluorescent lamps and bulbs cease after July 14th 2012.
The phase out of T12 bulbs was a part of an effort to encourage consumers to use more energy efficient lighting such as LED bulbs.
If you put a T8 bulb in a T12 light fixture the light will work although the T8 bulbs will not last as long because of the higher current going through the T8 bulb.
You can use a T8 bulb in a T12 fixture but you must bypass the T12 ballast by removing it completely and replacing the T12 ballast with a T8 ballast.
A T8 bulb ranges in length from 18 inches long to as long as 2ft long to 3 ft long.
The length of a T8 bulb that has a lamp code of F15T8 is 18 inches.
The length of a T8 bulb with a lamp code of F17T8 is 2 ft.
And the length of a T8 bulb with a lamp code of F25T8 is 3 ft.
T8 bulbs also come in lengths of 4 ft and 5 ft.
The T in T8 bulbs stands for tubular and the number 8 indicates the diameter of the bulb in eights of an inch.
T8 bulbs have a diameter of 1 inch.
T8 bulbs are being discontinued.
T8 fluorescent bulbs were discontinued and phased out in August 24th 2023.
The production and imports of T8 fluorescent bulbs are also banned in the EU.
The phase out of T8 fluorescent bulbs is a part of a global effort to reduce mercury pollution and CO2 emissions.
Fluorescent bulbs use almost twice as much electricity as LED bulbs do which are more energy efficient.
You may be able to find some in some stores that still have them in stock or online but T8 bulbs are no longer being manufactured.