I've designed a set of diffusers to work with these clip on desk lamps off amazon (Xtricity Desk Lamp on Amazon).  Outer diameter of lamp was ~109mm.  You should be able to scale the XY to fit other sizes. Z of diffuser face is ~.3-.4mm.  This seemed to be an ideal thickness for light diffusion.  There is a simple round version, and a larger "lightbox" square version.  Both seem to work quite well.  I use them to light up my standing desk when I teach Zoom classes from it.  Printed with white Hatchbox PETG on a Mini+

Print flat side down.  No supports should needed on either.

Update (12/24/21): Added the fusion 360 file so folks can resize to fit other lamps.