I know the T5 bulbs are a 5/8 inch diameter and T8's are one inch. There are commercial adaptor kits that fit over the end of T5 tubes to fit them in T8 sockets with the addition of a new starter. These seem mainly for offices etc and I was hoping someone may have done a conversion for an aquarium. I was also hoping to use the LED
style lights as these last longer and use less electricity but some websites suggest they wont give out the same illumination as a standard HO
T5 unless you get the wattage right. Cheers.