The app, which requires root access to work, reflects the rhythmic punctuation of songs on your smartphone’s built-in LEDs. As the app is currently configured, a single LED alternates between three colors (up to three work synchronously).
The developer has posted handy videos to illustrate the effect on a few different devices, one of which you can see in action below:
LED Music Effect supports a nearly endless list of music players, including but not limited to Google Music, Spotify, Rhapsody, and Poweramp. The developer has only tested the app on a few devices, namely Sony Xperia phones, but is confident it’ll work on most smartphones.
The app is listed as a free download on the Google Play Store.