The audience members at a rock concert should be able to download a simple application to their cell phone, and register this through a simple GUI. Behind the artist on stage there is a screen, with a simple camera on top. The camera is taking pictures of the audience. At special occasions the audience will be instructed, by the artist, to hold up their phones with the screen towards the stage. The mobile is a replacement for the lighter.
On control a signal the application will fill the entire mobile screen with a single color. The control signal can as an example say: " all pixels white". The signal will be specific for each application. Each mobile will be a pixel in a larger picture, which will be presented on the big screen. What kind of picture the audience can create will depend on the number of people in the audience.
As a motivation for the audience to hold up their phone, the camera on top of the screen will take pictures of the audience. In that way the audience can see a reflection of them selves, and see what kind of picture they are creating together.