How might someone go about shortening a shop light, making a 48" into a 36" light fixture?
It can be done. First, buy a variable-speed Dremel.
Then check out this post:
It really depends on your being able to visualize the finished end of whatever shoplight you intend to shorten. It helps to be mechanically inclined.
I've found you need a very sharp saw blade to cut through a fluorescent tube :)
Shrubs_n_bulbs brings up an important point. Shortening the bulb is an acquired skill. I use only a "full spectrum", High CRI, phosphor compliant tube chisel for this. Practice this first, as your will be asking your neighbor for more lamps when you run out of yours.
To reseal, remember: There is no better substitute for Duct Tape than Duct Tape itself.
Hope you know those last two posts are just joking around.