Depends on the tube and who you ask. There is little fundamental difference between the best T5s and the best T8s. All T5s have pretty much the same performance. Some T8s have comparable performance, although in different sizes and powers making it hard to compare, but some T8s are frankly awful. The one area where the T5s win convincingly is getting the maximum light from the most compact lamp.

I don't fully understand your answer, are you saying that I should stick with my T8's because the T5 are esentially the same? What about heat production?

Kyle

I don't know what T8s you currently have so I don't know whether you should switch or not. "T8" is not a specific tube, it simply describes the thickness of the tube, some T8s are very good and some are very bad.

Total heat production from a T5 is comparable to the heat production of a good T8 of the same power (although they are not generally manufactured in the same sizes or the same power levels), while the light output will also be approximately equal. The T5 will be hotter to touch because the heat is being produced from a smaller area. A "bad" T8 of the same power will also produce the same total heat but significantly less light.

T5 bulbs are more economical than T8 bulbs since they use less watts and put out more lumens or light. However, T5 bulbs do not fit into a fixture designed for T8 bulbs if you were thinking about replacing your T8 bulbs with T5 bulbs then you would have to get a retrofit kit if you don't want to buy a new fixture. The retrofit kits are pretty cheap and pay for themselves after a few years of use from the energy savings and you can find a good kit from Lumiversal at www.lumiversal.com