How to Use the Fluorescent Tube Size Guide
Fluorescent tube codes like T5 and T8 look cryptic, but the number is simply the diameter measured in eighths of an inch — so a higher number means a fatter tube. Select a tube type above to see its diameter, typical fluorescent wattage for a standard 4-foot tube, and the wattage range a comparable LED replacement usually needs.
T5, at about 16mm across, is the thinnest and most efficient of the three, producing similar brightness on less power — it's common in newer construction and retrofits. T8, roughly 26mm, is the most widely installed size in offices and homes today. T12, the oldest and thickest at about 38mm, is far less efficient and is increasingly being phased out in favor of T8 or LED tubes. When switching to LED, matching the diameter and length is only half the job — many LED tubes also require removing or bypassing the fixture's existing ballast, so check the packaging before installing.
Frequently Asked Questions
The number refers to the tube's diameter in eighths of an inch — T5 is about 16mm (5/8in) and T8 is about 26mm (1in). T5 is thinner and more efficient, producing similar brightness with less power.
You can, as long as the diameter (T5, T8, etc.) and length match, but many LED tubes require removing or bypassing the existing ballast. Check the product's ballast compatibility before installing.