Bulbs are 5" from the surface, 24" from the substrate. 4x 46" bulbs (54w) Bulbs are probably 3/4"-1" from each other. Also the zoo med flora sun pink bulb i swapped for one of the 6,500k in my fixture seems to have a bit of effect on the plants this morning... the plants are maybe 8"-11" tall and the tops of the leaves are turning red again it seems.