I ran the numbers several times and just could not justify purchasing T-5's or even T-8's over the old T-12's. The T-5 bulbs were 8 times and the fixtures 3 times the price. It would take over six years to make up the difference in energy savings. And that's assuming the bulbs never need to be replaced.
I use the T-12 bulbs in tight over young seedlings. When it's time to transplant, the larger seedlings go under metal halide lights (I lucked out and got these fixtures for free - rescued from the trash).
I keep the window open at night to try to get the temperature under 60°. I also try to give all seedlings at least 30 minutes per day of fan time to stimulate stalks to strengthen.
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