German maker Helmut Wittek created a fake window to brighten up a windowless room. It has white, yellow, red, and blue LEDs triggered depending on the time of day, creating a sunrise at dawn and a sunset at dusk. The video shows the effect sped up, 3 seconds per hour.
This tutorial describes the building of a fake window which is illuminated by superlight LEDs in different colors. These are controlled by an Arduino microcontroller board so that the current daytime is reflected by the light mood.