A while back I got the idea to design a floor light that could be turned on/off from 1 switch. So, with little prior skill or knowledge of redstone, I decided to try for it. I suceeded thanks to pistons, though it's hardly efficient resource-wise. It's largely a waste, but it works.
I turned it into a cieling light for the video so that I could show the workings of it without having to build and dismantle an entire room.
I also made a tutorial for any who wish to make one: