In the past, buying light tubes for fluorescent lighting was relatively simple and uncomplicated because a large majority of the fixtures simply used the T12 ballast and tubes.
Now, with the use of LED tubes but the continued use of the some of the older T8, T10 and T12 ballast systems it can be challenging to know just what type of tubes to use. This can be further complicated if you have some new fixtures and some older retrofitted fixtures that may all need different tubes.
Size of the Tube
The actual size of the diameter of the existing tube will be marked on the end of the tube. In some cases, or if the tube is old or damaged, it can be difficult to read. However, each of the different sizes will have a specific diameter measurement. Simply measure across the base of the tube, between the two pins, and you will know immediately what size of LED tubes you will need.
The largest is the T12, and the measurement of the diameter will be 1.5 inches. The T8 is the next largest with a diameter of 1 inch, and the T5 is just 5/8 of an inch. It is important to measure as it is difficult to estimate the T12 and T8 diameter unless you have them side by side to compare.
Ballast Types
There should be information on the fixture with regards to the ballast type. Generally, the T12 tubes will be used with magnetic ballast or a bypass, and the T8 tubes will require an electronic ballast.
You will also find that you will have a specific type of lampholder, most often called a tombstone, that may be shunted or non-shunted. The non-shunted are sometimes called rapid start, and they offer several savings over the long-run in the life of the tubes as well as the life of the fixtures.
If you do have a newer fixture, it is likely to require an electronic ballast, and this makes finding the right LED tubes much easier. These will accommodate for any of the correctly sized tubes on the market today, and most tubes will list a variety of the ballasts that they are fully compatible within.
There are also new types of LED tubes that are known as hybrid tubes that can work with the traditional type of ballast or with the new electronic ballasts. These are a bit more costly but for commercial applications they may be the best option as they can continue to work through the bypass function even if the ballast happens to fail.