I use T8s...two banks of two double fixtures. 8 tubes (6500k) for a total of 256w. This covers an area approximately 2' x 4'. (31x51) close enough.
These fixtures were old T12s with magnetic ballasts, but I converted them over to T8 by installing the electronic ballasts and rewiring. It was the cheapest way out two years ago when I did the job. But hey, they're doing fine, giving me more light for less wattage...256w vs. 320w.
I use window chain and pins to adjust them. The enclosure is covered with 1/2" rigid Thermax insulation with reflective Mylar inside. I keep the whole shebang in an unheated room and the plants stay between 62*-70*.
Works well for my needs.
Charlie
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