I have built 3 light boxes for stained glass panels.  All of these had zero clear glass, or just clear glass on the outside border.

If you have clear glass more towards the center of the panel, then you are more likely to see the bright rectangles of the LED strip lights.  This sketchup view illustrates this.

One could effectively move the LED light strip farther outwards, if one expanded the size of the box.  Of course, this takes more space and cost for more wood.

Another option would be to make a "wood dam" that would block the view of the LED rectangles on the strip.

The only problem with this idea is that the wood dam or strip, might block too much light from illuminating the panel. Will have to try it out.

When I went to screw the box to the front frame, I marked the frame on all 4 sides at 1/4" from the outside edge, to properly place the box on the frame.  It didn't work.......measured and found I had 7/16" overlap versus the desired 1/4"........this should still work ok.

Checked spreadsheet and found error.  When I calculated the box outside 2 dimensions, I subtracted twice the overlap number (how much I want the front board to overlap the stained glass), instead of subtracting twice the 1/4" overlap I wanted.  I fixed the spreadsheet.

I learned many years ago that my brain does not think conceptually in 3D very well.

When I got the box built and the SG panel set in place, I decided to make the dam 2 inches tall, and 1/2" thick.  If I keep the LED lights below 2" from the panel, then in theory you should not be able to see the bright lights.  The only thing I don't know is if enough LED light will get to the stained glass panel.  Oh well, just try it and see :)

If I make a bracket on the outside of the dam, I can screw the dam to the frame, and it will also hold the SG panel in place.

I got 3 wraps around using LED tape.  I tried it using just 1 wrap, and I did not think I had enough light (by temporarily putting the assembly together), so I used all the 16.4 feet which has 300 LED lights.

My initial dam only allowed about 3/8" gap for the light to cross from the outer area into the center panel area (2-1/8" tall dam minus 2.5 " side height = 3/8").   I did not think I had enough light to the center of the panel, so I removed 1/2" from the top of the wood dam.......which should give a gap of...... 2.5" height minus 1-5/8 = 0.875 or 7/8" air gap.  I used the radial arm saw to remove the 1/2" of material from the top of the wood dam.  I had to paint the cut part white again.

The next photo is with the shop lights on and the LED at max brightness...............

To my eye, I got a better and brighter result in the center of the panel.  The dam is still higher than the top of the LED strips, so you can not see the bright spots.  Unfortunately, a photo of video will not show the difference, as I have learned on past projects.

You can use this link to download my Sketchup design.

You can use this link to watch a video I made about this project.

With 3 wraps around of the LED strip light, and having them spaced as close together as possible, it looks like the wood dam height should be about 1-5/8" inches tall.

I am glad this experiment worked ok, because it means I can LED light other stained glass panels that have a lot of clear glass in the center area, and you won't be able to see the bright LED emitter chips.