Allow me to try this approach then.
I'm figuring I purchase 28 of these:
http://www.homedepot.com/p/t/100192...&productId=100192753&R=100192753#.UnKX8PkSih0
Putting two per truss on 14 trusses. (spaced 4'8" from wall, 4'8" between both, and finally 4'8" from other wall)
Then purchasing 4 boxes of these:
http://www.lowes.com/pd_291833-3-22...l=1¤tURL=?Ntt=t8+fluorescent&facetInfo=
This scheme would use the same number of F32T8 tubes as I previously suggested using four twin-tube fixtures per truss; and thus, the total light output would be the same at the source.
HOWEVER, given your open-truss ceiling, those fixtures will effectively waste a LOT of their output due to the lack of a reflector. And therefore the overall result would be FAR less successful. Do not underestimate this effect. For example, even if you were to use only three of those fixtures I previously suggested (or similar) per truss, that would surely put MORE light down on the shop floor. In addition,. you would lose some potential switching flexibility, vis-a-vis separate 4-foot fixtures. And finally, the inter-fixture spacing along each truss is also somewhat greater than ideal; but that's the least of the issues.
All, in all, color me unimpressed.
Each bulb produces 2800 lumens, so there is a total of 11,200 lumens per fixture. 11,200 lumens per fixture times 28 fixtures equates to 313,600 lumens, divided by 1800 sf that puts 174 lumens per sf.
174 lumens / sqft is actually overkill from what I have read on this forum...
Yahbut... That 174 lumens/ft.^2 is the total nominal light output AT THE SOURCE. Problem is, you're not working sixteen feet in the air. By the time the light gets down to "working height" (typically about three feet off the floor), you lose quite a bit (figure a third or so) of it, even presuming that ALL of the lamps' output is directed downward (which it wouldn't be, especially given those reflectorless fixtures you cited).
so would my approach work?
FSVO "work", sure. But it would certainly not work AS WELL as the approach I previously suggested.
Obviously I will have them switched, my goal being either 2 zones (left and right) or 3 zones (first 5, middle 5, rear 4.)
In a shop the size of yours, "zoning" may well be appropriate. But in addition to that, you will near-certainly ALSO want some control over the illumination levels WITHIN those zones. I typically recommend a three-bank approach, with "Bank 1" being a minimal level of "walk-through" lighting, "Bank 2" comprising about 1/3 to 1/2 of the remaining lighting (which, in combination with "Bank 1", provides sufficient light for non-critical work), and "Bank 3" being the remainder (used when you want maximum lighting quality/brightness). Obviously, you still want the light to be as evenly distributed as possible even when only some of these banks are powered-up; so this is yet another reason to use individual twin-tube 4-foot fixtures, so that the "banks" can be "intermixed" on an (approximately) alternate-fixture basis.
Hello NP Carling,
My building is similar to height as yours 14'5 at eaves but 20 at the top of the A frame in an open steel truss design. I'm considering using these fixtures below at home depot. I viewed the ones you attached in the prior post and also viewed them in person at home depot, I wasn't all that impressed with the amount of light thrown.
Nor would I expect you to be. They simply aren't appropriate for either open-truss or "high-bay" applications (let alone both at the same time).
I was impressed with a fixture they had that contained 6 T5 bulbs wow that was bright and the price tag was shocking about $80+. A bit too expensive for the number of fixtures I would need.
Maybe we live in different worlds; but I would not consider $80 out of line for a six-tube T5HO "High Bay" fixture. In fact, I'd be suspicious of the build quality and ballast(s) in anything significantly cheaper. That said, I would also seriously doubt that such a fixture is the best solution for either you or the OP, regardless of cost.
I did notice that it had a silver or chrome backing, which I think made a huge difference to the other fixtures in the store.
Probably polished aluminum or similar -- and yes, such reflectors are de rigueur in "High Bay" fixtures.
My plan was to purchase the 4 light T8 fixture below using 5000k tubes... but spraying the gray liner chrome or silver, something that will reflect.
High-gloss white would be your best bet. But you shouldn't expect that to be anywhere near as effective as a factory-installed polished reflector.
The big bonus here with this fixture is that it has a female plug built in therefore less wiring if you plan to daisy chain two together.
I don't consider that a "bonus" at all. In my book, the fact that these are "plug-in" shop lights, as opposed to fixed-mount units designed to be permanently installed, is a huge
DISadvantage. First, it means that (per code) all of the outlets these lights plug into MUST be GFCI-protected, even if they're 20 feet in the air. How often do you want to climb that ladder to push the little button after it trips? Second, having a rat's nest of plug-in cords hanging from the ceiling and/or fixtures will look ugly as hell, not to mention comprise an immense dust/dirt-catcher as time goes on. Also, plug-in connections are NEVER as secure as hard-wired ones. Do you ever get birds (and/or other critters) in that barn? And finally, I'd wager that those fixtures are NOT suitable for mounting directly to the ceiling/trusses, due to heat issues (hence the notation that they are to be suspended by the supplied chains) which will further exacerbate the wiring mess.
My shop is 30x36 and I was planning on 12 fixtures evenly spaced.
You, too, would surely be better off with a greater number of twin-tube fixtures similar to the ones I cited earlier.
