I was thinking of starting my seedlings this year with either grow lights on a rack or rope lights in sand. Q's I have been thinking about are:
Is one better than the other?
What air temperatures could these methods sustain - meaning could I put them in my greenhouse even though the air inside could get below or near freezing? Would bottom heat or grow lights keep them warm enough? Or should I opt for my uninsulated garage which probably gets only as low as 40 or so? I'd just as soon not have to take up space in my kitchen or some other living space. I need to grow a few thousand plants at least.
I'm afraid that once the seedlings are up that the leaves would be too cold without supplementing heat in the greenhouse at night, even though I could keep the soil warm enough.
I suggest you read the labels on the seeds you are planting. Many will not germinate if they are colder than about 60F. Some, like tomatoes and peppers prefer it to be closer to 80F. I doubt that a greenhouse that drops below freezing can be heated with grow lights or rope lights. There might be some hope for the garage, maybe. But I'm guessing some supplemental heat will be required there, too.
Thinking out loud: One thousand plants in two by two containers would take up four thousand square inches or about 576 square feet. Assuming a four tier rack system that's 144 square feet of floor space. If you use those 2 ft by 4 ft racks that you see at Gardener's Supply, Jungs Seed, or Territorial Seed, that would be 18 of those rack systems. Four light fixtures each, at 40 Watts each, 160W x 18 = 2.9 kW. The rack systems run a couple hundred bucks a piece. And the electricity, at 29 kWH per day will run about $50 a month.
Probably, in a well insulated space, this amount of heat will materially affect the temperature of the space.
I couldn't get a lighting salesman to tell me whether rope lights are incandescent or LED. But if they are incandescent, you'll use about five or seven times as much electricity, and my need to air condition or ventilate the space.
Correction: those racks are not two feet wide, more like sixteen inches. So increase electricity cost by 50% to $75 a month.