you can use plenty of different LED strips. here are two that I've liked. the first is used in these pictures. one is a COB LED set with a wall plug that's a bit nicer and more expensive and the other is a 2 pack (USB) that's a better value but not quite as bright. these are affiliate links for reference

Lam(MS)pen COB - https://amzn.to/3MJfSVU

Enqiqi - https://amzn.to/40GpLJB

if you need a USB wall adapter I use this pack - https://amzn.to/3ufIyzv

I have 2 cutouts in the back for 3M command adhesive strips on this. in the event you don't have any laying around you can order some here - https://amzn.to/3QYvSGb

three different bottoms. one has a separate component that you can color white for some internal light reflection. the two pictures below contrasting this had their exposure adjusted and are meant to really show the difference. I find it helpful but not a massive game changer.

• plain black back:

• back with white layer:

another decent option if you're going to keep the lightbox near, but not mounted against the wall is to punch some negatives/edit the file and cutout rings in the back for a nice backglow. I'm holding the sign a few inches away from the wall here:

comparison photo with it laid against the wall:

sometimes you get wisps of filament depositing places they shouldn't (ie. black strands showing up in white space). fixing those will be some trial and error but here are some tips:

• fully clean your bed
• fully clean your nozzle
• print the first layer a bit slower
• increase retraction slightly
• lower printing temps, within reason, for example I print pla close to 200 for these instead of the 220+ you'd normally be doing
• set your colors to print light to dark (see below). there's a button in the slicer to the right of the build plate that you can re-order your first layer. as far as I can tell this only applies to layer one unfortunately, but it's still helpful
• disable "reduce infill retraction" if you're using orcaslicer. idk if it's in bambu studio
• enable "avoid crossing perimeters" and set an arbitrarily high value (200mm or something)
• if you can, pause at the end of each of the first 4 layers and manually remove and errant filament strands