If you're doing 12/12 from seed you can end up with a tiny worthless plant sometimes. It's better to veg and trim or tie it down if it gets too big, or do 12/12 with larger rooted clones than to do this from seed.
You never know what you'll end up with this way. Take some clones and try normal veg with them to compare.
If you want them short with short spacing CFL's seem to win at that. CFL's really keep them short and bushy with very tight node spacing if you use them right and not too far away. Compare a few clones under CFL with normal (but short) veg times. As in two weeks of good veg growth, or longer if they're growing slowly.
Here's what can happen with 12/12 from seed... Look at the pic, you don't want this, it's already flowering and you can see it just won't yield crap: