I don't think you're giving us the info that we really need, but to answer your question...

I use (1) 4' fluorescent light fixture (with 2 bulbs per fixture) per every 2 square foot of growing area (three fixtures per 4' x 18" shelf). Some get by with less, but that's what works best for me. I use the cheap (just under $20 at Home Depot) shop fixtures with the small side reflectors and 5000K bulbs.

Yeah like Brandon said, foot candles isn't the issue and "at center" is only relevant if you have 1 plant sitting right at center. For the bulbs you describe, 1 " above max. or close enough that they are just above brushing the tops of the plants.

What determines how many fixtures you need is the sq. footage of the plants you are trying to light up.

Dave

Thanks guys for taking the time to chime in! Soooo, I guess I should have asked my question in layman format...... :)

Here goes........ I need to know if the light set up I'm using is sufficient. It's Lowe's 4' 4 bulb fixture with T8s (F32 T8/741, 32W, 4100K).

Here's a pic of one set up...... Shelves measure 16"D x 4'W

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Is this close enough to the plant?

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Ok so you have approx. 6 sq. foot of shelf that needs coverage. Assuming the 4 tube fixtures are also approx. 16" wide then you also have an approx. 6 sq' light footprint MINUS the loss caused by the ends of the bulbs.

So depending on bulb spacing (some fixtures have a wide center dead zone - 2 bulbs, a bare space, then 2 more bulbs) it is probably sufficient except for the darker ends of the row. But then you just need to rotate the trays now and then to compensate when you notice them leaning toward the center.

If the fixture is only 10" wide (I looked at several Lowes fixtures) then you have approx. 2-3" down each horizontal side of the shelf that will have the same problem as the ends - less exposure - plants on the ends of the trays will lean in. So you turn the trays parallel to the shelves to compensate for that.

Closer to the plants will also reduce the light's footprint but with T8 rather than T12 they should be close enough based on the pics. When time to replace the bulbs look for higher number K if you can find them. That will let you raise them a smidge more and increase the footprint.

OK?

Dave .

Thanks soooo much Dave!!! I have been rotating flats for better light exposure.......

I should mention I have a (NEW) 6 x 8 heated GH, which brings up another question ..... When can I move seedlings (that are under lights) to GH ?

If it is heated then any time assuming you also have some sort of venting system. Sunny days will cook anything in the GH quickly with out good exhaust venting. It was 70 here today but 110 in the GH until I got the auto fans and exhaust system back on line and that was with 80% shade cloth on too.

So cooling quickly becomes more of an issue than heating as long as you can keep it above 40 at night.

But moving under-light-indoor-plants out to a GH is still a big environmental change so it still requires some gradual acclimation.

Dave

Good job on the rack cugal! I use those same racks in my seed room.

Thanks again Dave! Yeah, I have two auto roof vents that are set to open around 75F as well as a fan for circulation. I also need to devise a small exhaust fan......

And yes, I'm amazed by how quickly my el cheapo triple wall poly carbonate heats up!

1500W infrared heater keeps it 60F at night, sans any crazy Kansas weather..........

Guess I need to get my shade cloth back on, uh? Took it off for the winter.....

Soooo.......... Are plants hardened off when they come out of the GH?

Thanks brandon 7! Yupp those are Lowe's specials...... LOL Practical though... Wheels are a must.... Makes transporting from shop to GH a breeze!

Soooo.......... Are plants hardened off when they come out of the GH?

Somewhat but not fully. Temps, usually, yes. But not to wind exposure and most triple wall cuts UV sun exposure by 30% so exposure still needs care.

Dave