This is a simple idea which has already led some local artists to make shiny balloons to light up a pier, and has inspired a teenager to start a business and win various entrepreneurial and inventing awards with something that leaves most open hardware or electronics enthusiasts cold and blank.
Basically the most simple thing you can build using electronics is an LED attached to a resistor, and both ends of those two, attached to a battery. Another simple variation on this is the throwie, which is LED + Battery + magnet (so it sticks to what you throw it onto).
To many this is old stuff, far too simple to be interesting any more, but to me the simplicity of the design is beautiful:
But it's actually a lot more fluid than that picture, made of bendable wires that could go anywhere, and could be arbitrary lengths really.
LED light can be very directional and will project really nicely on to things, so an LED tree made of wire or pipes that you can position seems a good idea. …