I started my tomatoes indoors 10 days ago,and the seedlings are starting to grow up. I keep a light breeze on them for 6 hours a day and under a lamp for 12 or so hours a day.

I use a Fluorescent T8 light fixture with a 'Daylight Deluxe' lamp rated at 6500k color temp.

How many hours a day should I leave my seedlings under the lamp? I've heard conflicting advice, and wanted to hear from someone who does the same as I do.