After finishing, I discovered another artist's elegant take on the burnout concept here: http://www.castordesign.ca/
I also realized a number of shortcomings upon completion; namely, the tubes being buried permanently in concrete makes it difficult to replace a broken bulb or to move the lamp without threatening the tubes. The next iteration, perhaps, will have sockets which facilitate swapping out the tubes for transport or repair. In the process of making the lamp, one tube broke; I've included replacement instructions here.
Fluorescent tubes are filled with hazardous toxins, namely mercury. Work in a well-ventilated area, and wear a mask if you break a tube. Clean up the shards of glass with gloves.
Salvage the bulbs from your office, home, or school. Counties and towns with bulb-recycling programs might be inclined to spare a few if you ask nicely.
You will need these materials:
eight 1-1/2" dia.burned out fluorescent tubes
8" dia. sonotube or similar
approx. 2' square of 3/4" plywood
approx. 12" of 2" dia. PVC pipe
50 lbs. quick-set concrete mix
three-wire grounded power cord
approx 3" x 6" x 1/4" piece of plexiglass
You will need these tools:
1-1/2" drill bit
2-1/4" hole saw
Dremel tool or similar
Step 1: Formwork (1)
On two of the circles, lay out eight center points in a radial pattern. Start by pulling one line across the circle, dividing it in two; then measure the center of that line. Take a square and pull a line perpendicular to the first, dividing the circle into four equal pieces. Subdivide again, just like cutting a pie, to create eight even pieces. Measure up each line 2-1/2" from the center and make a mark. Drill each mark with a 1-1/2" bit. Make two identical pieces like this. On one of them, drill out the center with the 2-1/4" hole saw bit.
Cut the two drilled-out circles out of the piece of plywood they are in. Cut them large, so they will rest on top of the sonotube without falling in. Cut the third small, so it will fit inside the sonotube.
Cut the PVC pipe and the sonotube to 12" long. Sand and smooth the pipe's cut edge.
Set all these pieces aside for a minute.