My fixture is 24x19.I have an 8 bulb t-5 setup that I absolutely love however, it does not fit within the shelfing that I use (4 ft wide, 18 in deep chrome wire shelving). The shelving dimensions include the posts of the shelves so there really isnt 48 or 18 inches of room at the corners. A 6 bulb setup would fit perfectly so I will purchase 2 of them the next go around. Yes I love the t-5's and the 8 bulb but want everything to fit nice and snug