Extract some victims from a square foot of glass tiles:

Wire an old WS2812 breakout board (the new ones are much larger) to an Arduino Nano running the Nissan Fog Lamp firmware:

Aaaand it looks like this might actually work:

The WS2812 “beam” illuminates the 25 mm square tile without too much vignetting at about 15 mm.
The bottom tile is white-ish, the top is gray-ish, and they look different enough to justify using only one color in each array:

Now, for some solid modeling …