Just a quick thought after looking at the picture. If the fan is a 6" fan and 75% of the fan is exposed on the other side of the light fixture bottom or reflector and the soil depth is 2" below the top of the containers that means the light is at a minimum 7" above the soil assuming the bulbs come all the way down your reflector to the bottom but I got a hunch the bottom of the bulbs are maybe 2" above the bottom of your reflector! That means the light is too high if you're using CFL's. Frankly, if you have access to a simple 40W fluorescent you can use that and place it about 1" above the top of the containers.