T12 lamp with a diameter of 38mm (12/8)",
T8 krypton-filled lamp with a diameter of 26mm (8/8)", and
T5 lamp with a diameter of 16mm (5/8)"
there are two versions for T5 lamps, high efficiency (HE) version and high output (HO) version.
The difference between of shape on the T5 & T8 was in the tube diameter and length. T5 is 15mm dia. x 1149mm long and T8 is 26mm dia. x 1200mm The luminaire was equivalent equal but the energy to be saved app. 28% in the T5 tube.