[Cinnibun]

Has anyone ever heard of T4 lights being used as a light fixture? I saw it on an ad and I wasn't quite sure if it was just a typo, and meant to say T5 instead

 

[jkcichlid]

Those are real bulb sizes. The number behind the T is the diameter in 1/8" increments. For example T8 is 8 X 1/8" or 1" in diameter. T4 would be 1/2" diameter. Not common yet but definitely coming into the market as T12, T10 and eventually T8 are phased out to to poor efficiency.