My youngest, being nearly 16, decided that his decidedly warped digger-themed lampshade was due for retirement, and asked me to make something to replace it.
Naturally, I turned to the laser cutter...
I designed the shade to fit a standard British pendant light fitting.
That meant it needed a circular hole, 3cm in diameter, in the top of the fitting.
I had a fiddle with a number of other lampshades in the house, and worked out that it needed an internal diameter of at least 8cm to be able to get my hand in and handle the bulb.
And, of course, it needed to be long enough to enclose the low-energy bulb.
I started with a radial-slat design, but it looked too Spartan, even for my minimalist tastes, so angled the slats. That small change seriously improved the look of the fitting.