Hi,
This is a lightbox for model railway buildings in various sizes to individually illuminate windows. There are different sizes so that there should be a suitable one for most windows. A 5050 LED fits perfectly into the hole. For the longer boxes, I glued some aluminum foil inside with plastic glue to act as a reflector. In my case, I used a WS2812B LED strip as it allows me to create various lighting effects with an Arduino. I have windows, like those in the butcher's shop or kitchen, where the light should stay on permanently. On the floor above, I have a restaurant where the light should also stay on permanently. However, there is a 25% chance that a disco mode will be triggered. When this happens, the LEDs will light up in different colors. In the floors above the restaurant, I have regular apartments where the lights randomly turn on or off. Since I chose a WS2812B LED strip, I only need to connect 3 wires to my Arduino Nano. You can find the code in the documentation.