Rod Serling invited any viewers to submit a script. He was flooded with over 14,000 scripts, and he actually got around to reading 500 of them. But only two were any good, and he couldn't use them because they didn't fit the format of the show.
All episodes in Seasons 1, 2, 3 and 5 were thirty minutes in length. Episodes in Season 4 (airing from January to May 1963) were one hour in length due to CBS' switching the show's available time-slot where only an hour could be taken.
Of the three "Twilight Zone" TV series over the years, this is the only one which does not include Rod Serling's image during the opening credits. Of course, this is the only one of the series to have the opening voice-over performed by Serling.
Due to budgetary constraints in its second season, the network decided to cut costs by shooting some episodes on videotape rather than film. Because videotape was a relatively primitive medium in the early 1960s, the editing of tape was next to impossible. Thus, each of the 6 episodes was "camera-cut" as in live TV, on a studio sound stage, using a total of four cameras. The requisite multicamera setup of the videotape experiment, pretty much precluded location shooting, severely limiting the potential scope of the story-lines, and so, the short-lived experiment was ultimately abandoned. The limitations of using videotape (e.g., it could not be edited as cleanly as film and its visual quality was poorer) led them to switch back to film for the rest of the series, despite the greater cost. The 6 videotaped episodes were titled: Twilight Zone: The Lateness of the Hour; Twilight Zone: Static; Twilight Zone: The Whole Truth; Twilight Zone: The Night of the Meek; Twilight Zone: Twenty Two; Twilight Zone: Long Distance Call and then transferred to film for broadcast, which saved the producers about $5,000 per episode.
Rod Serling thought he had come up with the term "Twilight Zone" on his own (he liked the sound of it), but after the show aired he found out that it is an actual term used by Air Force pilots when crossing the day / night sides above the world.
Series creator Rod Serling made up the phrase "Sixth Dimension" to use in season one's opening narration. William Self of CBS-TV asked him what was the fifth dimension (given that dimensions one through three are exemplified by a line, a plane, and a cube, respectively, and the fourth is time). Serling answered, "I don't know. Aren't there five?" He then changed the narration to "There is a fifth dimension..."
The Manhattan Transfer quartet released a pop vocal rendition of the series titled "Twilight Zone" (1979) using the original series intro music to open their song.