any deviation from straight line decreases the amount of light transferred. the manufacturer of the ones i used recommends no more than a 15 degree bend. the bell shape on the bottom of the tubes is actually a modified plastic planter from lowe's
they actually look better now than in the picture because i sealed all of the seams on the tubes and where they join the plastic bezel on top and bottom with calk that was smoothed to give the appearance of one solid piece. the bells are coated with reflective chrome paint on the inside to direct all sun rays down into the tank without letting them escape over the top edge.