In a

television studio A television studio, also called a television production studio, is an installation room in which video productions take place, either for the production of live television and its recording onto video tape or other media such as SSDs, or for ...

, a tally light is a small signal-lamp on a

professional video camera A professional video camera (often called a television camera even though its use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). O ...

monitor Monitor or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, West ...

. It is usually located just above the lens or on the

electronic viewfinder An electronic viewfinder (EVF) is a camera viewfinder where the image captured by the lens is displayed on a small screen (usually LCD or OLED) which the photographer can look through when composing their shot. It differs from a live preview ...

(EVF) and communicates, for the benefit of those in front of the camera as well as the

camera operator A camera operator, or depending on the context cameraman or camerawoman, is a professional operator of a film camera or video camera as part of a film crew. The term "cameraman" does not imply that a male is performing the task. In filmmaking ...

, that the camera is 'live' - i.e. its signal is being used for the 'main program' at that moment. For television productions with more than one camera in a

multiple-camera setup The multiple-camera setup, multiple-camera mode of production, multi-camera or simply multicam is a method of filmmaking and video production. Several cameras—either film or professional video cameras—are employed on the set and simultaneous ...

, the tally lights are generally illuminated automatically by a

vision mixer A vision mixer is a device used to select between several different live video sources and, in some cases, compositing live video sources together to create visual effects. In most of the world, both the equipment and its operator are called ...

trigger that is fed to a tally breakout board and then to a special

video router A video router, also known as a video matrix switch or SDI router, is an electronic switch designed to route video signals from multiple input sources such as cameras, VT/DDR, computers and DVD players, to one or more display devices, such as ...

designed for tally signals. The video switcher keeps track of which video sources are selected by the

technical director A technical director (TD) is usually a senior technical person within e.g. a software company, engineering firm, film studio, theatre company or television studio. This person usually has the highest level of skill within a specific technical f ...

and output to the main program bus. A switch automatically closes the appropriate electrical contacts to create a circuit, which activates the tally unit located in the

camera control unit The camera control unit (CCU) is typically part of a live television broadcast chain. It is responsible for powering the professional video camera, handling signals sent over the camera cable to and from the camera, and can be used to control ...

s (CCU). If more than one camera is on-air simultaneously (as in the case of a dissolve), during the duration of the transition the tally lights of both cameras will remain lit until transition completion. This is also the case when multiple cameras are placed in 'boxes' on screen, sometimes referred to as " picture in picture" mode (PiP) .

Colours & usage

Tally (also known as the 'on-air' indication) lights are typically red, although some cameras and

video switcher A vision mixer is a device used to select between several different live video sources and, in some cases, compositing live video sources together to create visual effects. In most of the world, both the equipment and its operator are called ...

s accept a preview tally signal, which is typically green. In addition to the tally lights, an additional light called ISO is sometimes used. ISO is the abbreviation for "isolated", and indicates that the video signal is isolated and recorded separately. When the camera's signal isn't used for the main program, but is being recorded for later

video editing Video editing is the manipulation and arrangement of video shots. Video editing is used to structure and present all video information, including films and television shows, video advertisements and video essays. Video editing has been dramaticall ...

, a yellow light indicates to the

that the content might be used at a later stage. So, although not 'on air', the operator should try to prevent making sudden moves etc. The ISO content is typically used for

b-roll In film and television production, B-roll, B roll, B-reel or B reel is supplemental or alternative footage intercut with the main shot. The term ''A-roll'', referring to main footage, has fallen out of use. Film and video production Films and ...

shots such as people's reactions when it's uncertain if, when, and how they will react. {{tv-tech-stub Film and video terminology Film and video technology Television technology Television terminology