Lost television broadcasts are composed of mostly early television programs and series that for various reasons cannot be accounted for in personal collections or studio archives.
A significant amount of early television programming is not lost but rather was never recorded in the first place. Early broadcasting in all genres was live and sometimes performed repeatedly. Due to there being no means to record the broadcast, or because the content itself was thought to have little monetary or historical value it wasn't deemed necessary to save it. In the United Kingdom, much early programming was lost due to contractual demands by the actors' union to limit the rescreening of recorded performances.
Apart from Phonovision experiments by John Logie Baird, and some 280 rolls of 35mm film containing a number of Paul Nipkow television station broadcasts, no recordings of transmissions from 1939 or earlier are known to exist.
In 1947, Kinescope films became a viable method of recording broadcasts, but programs were only sporadically filmed or preserved. Tele-snaps of British television broadcasts also began in 1947 but are necessarily incomplete. Magnetic videotape technologies became a viable method to record and distribute material in 1956. Televised programming (especially that which was not considered viable for reruns) was still considered disposable. What was recorded was routinely destroyed by wiping and reusing the tapes until the rise of the home video industry in the 1970s.
The ability for home viewers to record programming was extremely limited; although a home viewer could record the video of a broadcast by kinescope recording onto 8 mm film throughout television history or record the audio of a broadcast onto audiotape beginning in the 1950s, one could generally not capture both on the same medium until super-8 debuted in the 1960s. Attempting to film a television broadcast using the kinescope process required positioning the camera directly in front of the screen, blocking the view of other people trying to watch. This would have been very disruptive to the television viewing experience and as such home movies of this kind are exceptionally rare. Audio recordings, which do not require obstructing the view of the screen are more common and numerous copies of otherwise lost television broadcasts exist. The growing availability of home video recording from the late 1970s was also a benefit for television producers and archivers as video tape was now economical enough for a home viewer to afford and enabled television networks the ability to save much of their programming as well.