T5's are tube fluorescents. CFL (Compact Fluorescent Lights) are the ones you can plug into any socket so they are different. And the difference between T5's, T8's, and T12's has nothing to do with how good they are or how much light they emit. They all emit the same or roughly the same ammount of light. The numbers represent the circumfrence of the bulb so... T12= 12/8 of an inch or 1 1/4 inches. T8= 8/8 of an inch or 1 inch. T5= 5/8 of an inch. The only advantage of a T5 over a T8 or T12 is that you can fit more of them in the same space since thry are smaller.