This light bar mounts on the back of the X gantry and shines light directly on the current layer being printed. It was designed specifically for the Ender 3 Pro, but may work with other Ender 3s or any printer that uses a T-slot gantry bar. Be sure that none of the assembly extends below the nozzle Z position.

UPDATE - Version 2
After using the first version of this, I could see potential weakness at the right angle joint, and the bottom that covered the LED was mildly annoying. So I reworked it. Both left and right sides are now the same, and there is a wide version that will support the LED bar with a single mount in the middle if desired. The LED strip is not covered anywhere.
The original version is still available if desired.

After I got my Ender 3 Pro, I found it irritating that viewing the layer being printed (especially the critical first few layers) was so difficult due to the printhead being in the way and the shadow beneath. All the lighting solutions that I found were mounted on the top crossbar, which made the shadow even deeper. I saw that there was no reason that a light bar couldn't be mounted on the back as long as it didn't extend below the nozzle. After considering it for some time, I came up with this arrangement.

Many places have LED strips that can be cut to length, and I recently found that they are available for 24V operation. So I designed a slotted rail that would accept the strip and a couple of brackets that attach to the back of the X gantry using T-Slot nuts. The brackets are a snug fit on the ends of the rails, and the strip slides in from the end. Power is taken directly from the power supply terminals. The brackets are designed to be above the Z height of the current layer and the light shines down at an angle that illuminates the nozzle tip. So that critical first layer can be viewed in good light.

I have included a detailed construction document with pictures, and also the Fusion .f3d file if you need to make any adjustments or adapt to a different model printer.

The LED strips are readily available on Amazon, as is the 24 Ga. speaker wire, although together they will cost around $20. If there is interest, I might be talked into making wired LED strips available for moderate cost.... send me a message via Thingiverse if you are interested.

This is the first release of this design, so it should be considered a work in progress. Let me know of any problems with it.