In Incandescence you simply drum on the screen of your device with your fingers to keep to a rhythm. Doing so sets off a light show that becomes more and more intense the longer you can keep the beat.
It's a curious one, sounding like a mix of Beatmania, FantaVision, and Rez.
Here's the game in motion.
Incandescence is free, and available right now on iOS, Android, and Windows Phone.