|16mm - Color
Many catalogs file the film as "THX 1138:4EB" while the actual title states it as "THX 1138 4EB" (without colon). Further, the film was renamed with the additional subtitle "Electronic Labyrinth" due to copyright reasons prior to festival circulation (probably as the feature was conceived shortly after the first showings, see below). This renaming could be the reason why there's, in the beginning of the film, a difference in brightness of the title's lettering, between "Electronic Labyrinth" and "THX 1138 4EB", result of an additional photographic processing step.
After graduating from USC, Lucas returned to USC in a teaching role. With a group of students, as part of a course, he made THX 1138:4EB - intentionally meant as a "lighting test", as an exercise for his students.
In "The Making of THX 1138" (the feature film), Matthew Robbins recalls that "4EB", the "EB" stands for "earth born". In the same documentary Walter Murch states that the short film was based on a script he and Robbins had written, set in a dystopic world. When Lucas was looking for something to film, he asked them if he could base his film on this script, and turned it into an experimental short.
Contrary to popular belief, the film was actually shot on 16mm film and not on 35mm material. However, there were 35mm prints in circulation, made via blow-up. A very common source of false information stems from confusion with the feature film of the similar name - which is based on the short - as the feature was actually shot on 35mm stock. Also, the short was shot on color material, although the finished film has very little color in it.
After the film ran as part of a showing in UCLA's Royce Hall in 1967, George Lucas' film received the award of best picture of that night. Lucas came on stage to accept the award when a man in the audience stood up, introducing himself as an employee of Warner Brothers. The man told everyone in attendance that whoever would win this night's competition, his or her's film would be turned into a feature film at Warners. (as told by wayne-350 on http://www.imdb.com/title/tt0062331/reviews)