sorry for the delay in response i had it on its legs. and an open top tank so no real heating issues. The long sides are parallel to the the shorter sides directly across from them. and is around 23" apart. I would recommend no fewer than 4 bulbs of t-5 on that tank. They are really deep. But i used a current 2x24w on mine then i swapped up to a 75 gallon. With that depth i would definitely look around for a 250w pendant hung from the ceiling if possible. That's just my opinion. Its looking very nice though and watch out about them flat worms i was in a petstore when a lady brought some mushrooms in them on there and they were tearing the mushrooms up. Luckily the shop keeper saved the mushrooms. he used something like flatworm exit.