When can I put my babies under a light?

I just planted my seeds 3 days ago, this morning they just started to pop out of the soil. When can I put them under a light? I have a MH for veg. Should I wait until its a few inches tall or a few weeks old?

I would put themunder a T5 first, a little "lighter" on new growththan a MH. Turbo Pro

put the MH up about 3 feet and put them under right away. Assuming you have airflow in and out of your grow