I prefer grow lights personally. I use 4' fluorescent T5s suspended about the 10"x20" planting trays. I run two bulbs over each row of two trays and I try to keep the lights as close to the top of the plants as possible without burning them, usually and inch or two with the bulbs I use.
I find this gives the plants consistent "sunlight" for 18 hours a day and really helps them grow fast and strong. We have large south facing windows but we have large 150+ year old trees lining the southside that block a lot of the light coming in them.