Stephenson Blake advertised it as "just the right note for an advertising or display panel". Bitzer co-invented the flat plasma display panel in 1964. The interior of the booths are fitted with a large illuminated display panel. The lamps illuminated digits on a display panel corresponding to the number dialed. "Embedded DisplayPort" (eDP) is a display panel interface standard for portable and embedded devices. The plasma display panel was invented at the University of Illinois by Donald L. Bitzer.