(Credit: Yanko Design)
According to the writeup, the outside canopy that has a conductive membrane called PDVF. As rain hits it, the impact generates electrical energy that powers built-in LEDs on the umbrella. The harder the rain hits the brollie, the brighter the light. Now that's literally a brilliant idea, but the lights better be waterproofed, otherwise you'll end up as an electrifying light show.
Via Yanko Design