I use 6 -T12- 40 watt fluorescent lights only when they are under 6 inches tall.
Afterwards they bump up to 8-T5 bulbs, they stay under these until they are at least 12-18 inches tall.
Then I use a 400 watt Metal Halide for a couple of weeks, to get them ready to flower.
Then when their ready, I use a 400 watt HPS.