Is your LED lamp actually 90 Watts, or rated "90 Watt equivalent", or is it a compact fluorescent? To provide energy equivalent to sunshine, what you want is 50-75 actual Watts per square foot. If you have partial sun, then you could cut that in half.
Here is a blurb I wrote for a garden magazine awhile back on potting plants: PTP_2009_03_Pot_Culture
. If you're not in the western U.S., you probably won't find the Kellogg's soil, but regionally there are equally good choices.