I think that the only difference between the T-8 and the T-10 is the diameter of the bulb and the wattage. T-8 is 1" T-10 is 1 1/4" I find it great because you just place the unit on the top of the enclosure and then place the cap end in the enclosure and then you can use any length of bulb. The pet store here doesn't always have the 48" long, so the odd time I end up getting the 36" one. Also with this type of unit, since it requires 2 bulbs you can place one bulb in one enclosure and the other bulb in another unit as long as the enclosures are back to back/front to front. Also it will not work with only one bulb it need 2. But they also make a unit for just one bulb.