I've been doing some work in classrooms with various lighting
levels. One has .8 watts of florescent per square foot. Too dark
for old eyes, rough on young eyes and close work. One has 1.1
watts per square foot, ok for general work, not good enough for
close work. 1.3 watts per square foot in the machine area. Ok for
young eyes, not good enough for the over 50 crowd. My personal
shop averages 1.5 watts per sq ft with some brighter sections
over major tools. That is marginal, more fixtures are sitting in
the corner waiting for an install.

All of this figures that the fixtures have 180 degree reflectors
and you clean the bulbs now and then.

Jim Wilson wrote:

James B. Millard wrote...

I'm having a small shop built and am getting close to having to decide what
I'm going to do for lighting. the shop is 14'x18' and will house a
workbench a small lathe and mill and whatever else I accumulate...

I was thinking about flourescent lighting but I don't really have any idea
how much or exactly what optimum placement is.

Anybody have any ideas?



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.

14 x 18 = 252 sf; 252 / 15 = 17 tubes, or 9 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.

252 / 20 = 13 tubes, or 7 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 alternatives. You can
often get more uniform lighting by running a higher number of shorter
rows.

Jim