Sounds like you have a very good plan!

A 4ft. four-tube T8 fixture (with daylight bulbs) should provide good intensity & spectrum, and should also provide a good spread for your shelf size. Good reflectors would also add effectiveness for light output. Are you going to mount your lights so you can adjust the height if needed?

Yes, I'm going to hang the shop lights from chains so the height will be easily adjustable.

I intend to do...something....for reflectors, but don't have a plan yet.

Reassuring to hear I'm on the right track, thank you,
Kim

Thanks for taking the time to say thank you (often a true rarity on many internet forums)!

No, its just that 2 light fixtures are generally cheaper than 4 light fixtures - as in less than half the cost. There are several choices of 2 lamp bulbs that will fit in the space you have and run $15 or less apiece.

dual light fixture for T8 32W bulbs at HD

dual light fixture at Lowe's 7" wide

Dual light at Lowes 4.7" wide , but it's BLACK

That said - an advantage of the 4 light fixtures is that they SHOULD have a 4 light ballast in them, and for some reason those usually seem to draw less amperage than 2 - 2 light ballasts. Or at least SOME 2 light ballasts. Some that I have been looking at, for the 2 light ballasts the amperage is listed at .97A (call it 1A), but the 4 light ballast from the same manufacturer only draws 1.77 A at peak. On the other hand, the cheapy ballasts in my LOA 2-light fixtures only draw 0.8A.

So it depends on the ballasts in the specific fixture you are looking at.

Another reason to use 2-light fixtures instead of 4, 6, or 8 light fixtures is that it is possible to get 2 light fixtures that take up way less space than the multi-bulb fixtures. For example:

Dual bulb T8 fixture 2.75" wide

I think this is a MUCH better deal than any 4, 6, or 8 bulb fixture I've ever come across, because I can get FIVE of these in between the posts of my 18" wide shelves (that space is about 15.5 or 15.75"). I can put my 9" wide flats lengthwise on the shelves stacked 2 deep front to back - so about 4 total flats per shelf.

They cost $25 a pop, but I can't beat that even with a 4 light fixture. 10 bulbs over each shelf instead of just 4! Even if you're not trying to recreate the sun in your closet, you can easily space 4 of these fixtures across your shelves for 8 total bulbs. The only 6 and 8 bulb fixtures I've seen won't fit in the space I have plus they're expensive.

I don't know if these are over-drivable yet - but I hope they are. I have visions of getting the equivalent of 15 32W T8 bulbs over at least one shelf. I don't need near that for seed starting - but I have murraya koenigii that I need to keep healthy and happy indoors until spring rolls around again.

Lotsa lights are good. Great even. However you have to figure in the # of amps you will be drawing.

As long as you don't overdrive, with these narrow fixtures - which admittedly have no side reflectors, but who needs reflectors when you can have ACTUAL LIGHT? Anyway if you put 5 fixtures per shelf for 10 bulbs total

WITHOUT OVERDRIVING, you can assume that's a peak load of 5 amps - roughly 1 amp for each of the 5 ballasts in the fixture - for each shelf. That's with THESE ballasts; the ballast in the fixture you are looking at will be rated differently.

That is only 2 shelves you can have safely on a 15 amp fuse, assuming you have other stuff plugged into other outlets in the same room.

Such as - say - your computer. It's usually safe to assume that a computer is drawing around 5 to 6 amps - more at peak usage, if you're running graphics intensive games. So - you might want to take that into consideration when figuring the max load your circuit can bear - which is not actually the full amperage its rated for, but 80% for continuing loads - which is what your lights will be, and what my computer ends up being (eg its on for more than 3 hours at a time). So - aim for 12A of capacity for continuous loads.

Drop down to just 4 of these and you reduce the load to 4A per shelf. And that's still a heckuva lotta light even without overdriving. Some mylar or something to reflect back down to the plants might be in order because now there will be gaps between the fixtures in your 15.5-ish inches of space between the posts.

That said, the amp rating on a ballast is for peak load, not continuous load - eg it spikes high when you turn it on, then settles down and runs at a lower amperage. So you can reduce potential problems by putting each bank (each shelf) on a separate power strip and turning them on one bank at a time.

A printer also spikes - quite a lot in fact, for laser printers - when it turns on, and it goes to sleep when you're not using it. This is why I have the printer on a totally different circuit, its on the shared hall/spare bedroom circuit so its basically the only thing on the circuit. So it can spike itself off and on to its hearts content without affecting anything else.

So: Keep your printer on a separate circuit from your PC, and figure what your computer draws at peak - I'm pretty sure there is monitoring software out there that will tell you how much amperage your GPU is drawing, and that's generally the big load on your system (if you game anyway). Remember any other lights or devices in the room. Subtract that total from the 15A circuit that PROBABLY supplies your room. If you're lucky, it might actually be 20A. You better check your circuit box.

Whatever is left is how much space you have for bulbs. Then figure out what the draw is for the ballast(s) you want to run, and see if you have enough capacity left over to handle them.

Aaaand apparently I forgot to hit "submit" after hitting preview, but didn't close the window (fortunately) - so now, 12 hours later, here is the actual posting, LOL!

This post was edited by zensojourner on Wed, Oct 8, 14 at 21:54

Thanks, Zensojourner. I hope to someday have a light setup as badass as yours. Some of what you wrote is way over my head, but you raise a good point, that as I start to dream of filling my basement with grow shelves, I need to think about what my circuits can actually handle.

Just now, I did some circuit box exploration and determined that I'm lucky--- the only thing currently on my circuit is overhead lighting in the form of a single T8 4-light fixture.

This fixture I'm considering is more expensive than two 2-light fixtures, but only draws 1.5A:
Four-light fixture.

However, one advantage I see with using several fixtures per shelf is that I could potentially hang them at different heights if some seedlings grow markedly taller than others. I may experiment with that on one shelf....at the very least, use my old single grow bulb along with with a 4-light fixture.

Gotta remember that I'll also be running a small box fan to keep the air moving and strengthen those stems.

Thanks again.

You should have plenty of room to grow - electrical load-wise.

I checked our fuse box yesterday and found out - this is bizarre - that all of the bedrooms are on 15A fuses, the common bathroom and the laundry room share a 15A fuse - but there is a 20A fuse for the master bathroom.

Figure that one out. I can't. If that were my room, the separate stand up shower would already have been turned into a grow box, LOL! At least I'd have plenty of amperage for my super-shelves.

Zensojourner, I hear you. Even now, I'm thinking of far more things to grow than three shelves can accommodate...I could probably fill twelve shelves ;)