Easy to print and build light bar, that uses LED String lights.

The frame and cover pieces can be printed at whatever length will fit your build volume, and you can print as many of them as you want to get your desired length.  Just extend them on the long axis.

I printed the cover, frame and end pieces standing up.  Covers are printed in clear filament, but I think you could also use a white filament and print with thin walls.  I used the spacers to join the frame pieces together, along with superglue.  The cover pieces will slide on and should not need glue to hold in place.

My overall bar length is about 4’ and I used about 12’ of these lights attached to the frame.

https://www.amazon.com/dp/B0CGX9Y62X

For the end piece, I added a stop and changed the filament color to white on the rounded off section.  This is optional but gives the bar a more finished look.  There is also a thin section on each end piece that can be removed for the wire to pass through.