While rebuilding our house, it happened that the door of my sons room ended up at the other hinge side than planned. To my own supprise the only spare door was one with a glas window :

while this is nice in living rooms and hallways to spread some light, it's not as private and/or dark as you moght want it for privacy and sleeping. Buying a new door or appling a piece of wood instead of the glass was out of question, so we ended up with a quick duct tape and cardboard solution temporarily.

So we had some time to ponder a bit about which might a cool, nerdish or funny idea. That was about the time I stumbled over some cool coffetable LED build in ideas und alike.