18x18 isn't near big enough for one plant let alone 2 of them. My cab is a 6ft triangle and its almost not big enough for 3 plants. In the attached pics, there is only 1 plant in the cab.

There are 10 CFLs over the top and 10 dual tube 4ft flouro fixtures around the sides. I run the CFLs only till they get transplanted into 5 gal buckets, when they get put into flower, then I turn on the side lights also.