Tally light
In a television studio, a tally light is a small signal-lamp on a professional video camera or monitor. It is usually located just above the lens or on the electronic viewfinder (EVF) and communicates, for the benefit of those in front of the camera as well as the camera operator, that the camera is 'live' - i.e. its signal is being used for the 'main program' at that moment. Tally (also known as the 'on-air' indication) lights are typically red, although some cameras and video switchers accept a preview tally signal, which is typically green.