Spotty uneven light is what I don't want.
Good. Glad to hear it. HOWEVER... Now that we have "The Rest Of The Story", it is clear that the fixtures you currently have on hand are far from ideal in that respect. More on that in a moment...
Loft is 7ft high. 30" out from wall.
OK. So really, it's more of a glorified shelf than a real "loft", per se. That's fine as far as it goes; we just need to really know what we're dealing with.
Keep all my floor space for working. Only 18 wide, floor width is at a premium.
Understood, I think. From your earlier comments, I gather that at least most of the "under loft" area will be occupied by workbenches, toolchests, stationary tools, etc.? That leaves approximately 13 feet of "open" space in the middle, where you will presumably place any vehicles to be worked on, etc.?
Fixtures are 8ft in length total. I have 4 of them. 16 bulbs. 8 bulbs each side. 4ft t8 bulbs in fixtures
OK, obviously, that is a rather different situation than I'd gleaned from your earlier comments.
Four fixtures, each eight feet long, is inadequate to cover the full length of that center section, presuming two symmetrical "fore & aft" runs. That part of your shop floor is 26 feet long. So even using "best case" spacing, you're looking at "lengthwise" gaps of 2-1/2 feet at each end (which is not terrible in itself, if still wide of ideal) and five feet in the middle (which
IS terrible, especially in that most-critical "middle of the shop" location where presumably much of the work will be done). Had you gone with individual 4-foot fixtures, as previously suggested, you could easily keep those inter-fixture gaps down to no more than about a foot or so (which, with decent mounting height, would effectively "dissappear").
As I see it, you have two choices at this point...
1. - If those 8-foot fixtures are returnable, do so, and replace them with at least TEN 4-foot twin-tube fixtures. Put five of these fixtures in each of two fore/aft runs, with the end-to-end gaps kept as equal as possible, and no more than 1-1.5 feet (preferably less; you can **** them tight together if need be). Space these runs apart laterally by about 1/3 to 1/2 of the width of the "open" section (i.e., about 4.5-6 feet -- I'd probably lean toward the latter). Then augment this with additional task lighting under the "loft", as needed (the details of which will depend on more stuff we don't yet know)
2. - If the 8-foot fixtures are NOT returnable, then either use them for the under-loft runs, and do as above for the main section, OR... Add one additional four-foot twin-tube fixture to each run, presumably placed between the two 8-footers. This will bring the total "run length" of each strip back up to 20 feet; but you'll still have to live with somewhat larger inter-fixture gaps than would be ideal.
In BOTH cases (but especially the latter), mount these fore/aft runs as high as practical, so as to give the light the best chance of spreading out and ameliorating the dim spots resulting from the inter-fixture gaps.
Depending on the details of how you're going to use this space, there is also a possible alternative approach... Put the main runs under the very outer edges of the loft, all the way around, and again keeping the end-end gaps as small as possible. Then add ONE additional run centered between the other two and as high as possible (all the way up at the ridge line, if possible). This will provide somewhat better illumination of the sides of any vehicles parked in the middle of the space (which is likely one of the primary work areas), but require more fixtures.
