What is a T4, Anyway?

Microfluorescent T4 Light Fixtures in a pantry

There are some occasions when jargon from the lighting industry can go right over the heads of 95% of the population.  Ever heard of the term T4 fluorescent?  Or T2, T5, T8, T9, and T16, for that matter?  Felt a little out of the loop?

We’ll clue you in:

T stands for tubular, indicating the shape of the bulb.

The number following the T (2, 4, 5, 8, 9, etc) is the diameter of the bulb in eights of an inch.  So, a T4 lamp is 4/8” – or more simply, ½”.  The T8 is one inch.

If an HO follows the name (such as T5 HO), this stands for high-output, meaning these types of lamps are brighter and draw more electrical current.

If you can you think of any other lighting jargon terms we can clear up for you, let us know in the comments below.

Emily Widle

Emily graduated from UNC Chapel Hill with a degree in journalism. She enjoys scouring the news to report on the latest in the lighting industry as well as bringing valuable remodeling tips and exemplar home projects to light.