In a decision we completely agree with, these industrious young women decided that playing in the rain would only be more fun if it included an interactive light show. They wanted the rain itself to cause LEDs in their umbrella to light up. To achieve this, they put piezo sensors on each of the 8 panels of the umbrella. When that panel gets hit, its LEDs light up. You can see in the video after the break that it was quite effective.
Their next step should be to somehow increase the resolution to be similar to this one, while maintaining interactivity with the rain. How would you sense rain drops with more definition though?