When it comes to tubular lighting it can be confusing to determine which tube you require.  However there is a way that is simpler than it may appear - using the “T” number (T4, T5 etc.).  This determines the diameter of the tube so as long as the “T” number matches you cannot go wrong for matching the diameter.  This works for both fluorescent and LED versions.

What do each of these “T” numbers mean?

The "T" in this classification stands for Tubular. The number immediately following the "T" indicates the diameter of the tube in increments of one-eighth of an inch.

What are these tubes used for?

Depending on their size these tubes can be used for a wide variety of applications, here are some examples below:

T8 Tubes 

These are one of the most commonly found lighting tube types and commonly run on magnetic or electronic ballasts. Thanks to their larger diameter they have been found to be a sturdy choice for giving out a decent amount of light for the area required.

T5 Tubes 

T5 tubes are thinner and known for generally holding a higher amount of lumens per watt for the energy/wattage they use.  They are used for both standard illumination and taller spaces such as warehouses or as grow lights.

T4 and T2 Tubes

These tubes are smaller than their counterparts we have discussed above and for this reason are often used for compact and smaller fixtures where light is needed in a smaller space.  T4 tubes are commonly found in display lighting whereas T2 tubes are quite rare and will not often be found outside of specialist decorative applications.

Can I put a T5 bulb in a T8 fixture?

No, you cannot put a T5 bulb into a T8 fixture as they are a different diameter and have different pins at either end.  T8 bulbs use a G13 base which are spaced 13mm apart whereas T5 tubes have a G5 base which are 5mm apart.

Can I replace one of these fluorescent light tubes with LED tubes?

Yes you can, but some considerations will need to be made when installing the new LED tube.

All LED tubes should advise how they need to be wired in an accompanying set of instructions or with a datasheet that can often be downloaded from the manufacturers website by searching for the part number.

There are three main types of fitting your LED tube into your older fluorescent setup:

1. Ballast-Compatible (Plug-and-Play) LED: These LED tubes are designed to work with the existing fluorescent ballast (usually an electronic ballast). This is commonly referred to as retrofit and it should require no rewiring. However, it is worth checking that the LED tube you are purchasing is compatible with the ballast you have as the wattage the ballast can hold might be too high.
2. Ballast-Bypass (Direct Wire) LED: This style of LED tube requires removing the existing ballast and wiring the tube directly to mains voltage.  This removes the need to worry about ballast compatibility issues for the short and the long term.  We would highly recommend having this done by a qualified electrician.
3. Hybrid LED: These tubes can operate by being connected to a ballast or being directly wired to the mains making it a flexible option for installing your LED replacement.

In Conclusion

When purchasing a fluorescent tube of this type it is important to pay attention to the “T” number as this will help you determine the diameter of the tube.  You should not try to use a different type such as a T5 when you had previously used a T8 as it is very unlikely to fit without extra parts being required.  

It is recommended that you replace your older fluorescent tube with LED but when doing this it is important to check how the LED tube will connect with your desired set up and control gear.