Kudzu wrote...
I am getting close to wiring my new shop. It roughly 30 x 40 with 9 foot
ceilings. It a daylight basement but I have a minimum of windows. The shop
ended up more below grade that I expected. My plan once we get it dried in
to paint the walls white to lighten it up. Then install T8 fluorescent
lighting. I am going to look at 8' and 4' fixtures and compare prices to see
which is the better deal.

But my question is spacing and how many fixtures? I read somewhere to use
single bulb fixtures spaced at 4 feet. But so far that is all I have found.

In the shop, work surfaces should receive 100 foot candles from the
general lighting alone. A foot candle is one lumen per square foot.
Additional task lighting is often desirable at individual work stations.

The 100 foot candles is what you want *after* losses. The major sources
of loss are fixture inefficiency, lamp age, dust on lamps, and wall and
ceiling reflectivity. Together, 8-10' ceilings, 3' work surfaces, and
typical values for the aforementioned losses result in almost exactly a
50% reduction in the initial luminance of your lamps.

Fluorescent tubes typically supply 60-80 lumens per watt. A 40W tube, the
most common and cost effective option, typically puts out about 3000
lumens when new. Accounting for the aforementioned losses, each tube will
actually put about 1500 lumens on the work surface. Since you need 100
lumens per square foot, a tube will illuminate 15 square feet.

40 x 30 = 1200 sf; 1200 / 15 = 80 tubes, or 40 fixtures.

By the way, 40 watts per 15 square feet is 2.7 watts per square foot.
Some lighting designers use 2 watts per square foot as a lower bound,
which yields 20 square feet per 40W tube.

1200 / 20 = 60 tubes, or 30 fixtures.

For a rectangular area, you can run the rows parallel to the long edge or
parallel to the short edge. Sometimes the choice is dictated by other
design considerations, such as dust collection ducting or other
obstructions. If not, be sure to consider both ways. You can often get
more uniform lighting by running a higher number of shorter rows.

Incandescent and/or halogen lighting can be a good idea for areas where
you finish pieces that will be used indoors. Fluorescent lighting has
different color characteristics, and the color of a piece can "change,"
sometimes dramatically and unpleasantly, when brought from the shop to
it's final destination.

Jim