A "Filming in Progress" sign for our studio was recently requested to alert people when they should keep their noise level down, and refrain from entering the studio. Due to size limitations on the laser used to etch the side-lit "Another Teaching Moment" sign (see article), we had to use the glass provided in the shadowbox that was purchased, with a vinyl overlay. The tight fit of the glass didn't allow for the sign to be edge-lit, so backlit it was.
Initially the neopixels were placed on the back of the shadowbox, facing the glass in the blacked out area of the sign. They were so bright, that each individual neopixel was clearly visible. I then repositioned them to the back of the glass, facing the back panel of the shadowbox, but this was not distributing the light well enough. To fix this, paper was added to the back of the glass to diffuse the light, and aluminum foil was added to the back panel of the shadowbox to reflect the light back at the glass. This prevented the individual neopixels from being seen, but allowed the light to be evenly distributed and achieve the desired brightness.
The schematic is identical to the edge-lit sign, except there are a total of 104 neopixels in this strip. Aside from that, the only other difference is the enclosure. Instead of creating an enclosure for the trinket and components, they are just placed in the shadowbox. There is, however, an enclosure printed for the rocker switch, to allow for it to be placed inline on the power cable. The enclosure model was drawn in Autodesk's Fusion 360 and can be found here: https://a360.co/2Jzp7G2 and the cover here: https://a360.co/2JxNDqQ. If you prefer a premade enclosure, select one from this link: https://www.digikey.com/short/jz3p18 and modify as needed.
The code utilized was the strandtest example from Adafruit's neopixel library. I just changed the pin to 1 and updated the number of pixels used in the code.
This was a quick and easy project to add a much needed, professional looking sign to our filming studio.