The wristbands themselves are constructed of a thick fabric with LEDs inside the fabric. A radio receiver is located within a plastic piece on the band, and this receiver is able to get wireless signals from a controller, which is hosted on a laptop computer linked to a radio transmitter, which can remotely control the bands from up to 328 yards away.
Das sagt Wikipedia dazu
Also einfach LEDs die von einem Empfänger für Radiowellen (in dem blauen o. rosa Kästchen am Band) gezielt an- und ausgemacht werden... Und irgendwo im Stadion wird dann wohl ein Sender stehen der das ganze steuert.