- Inspiration for the Work: Barbara Clegg's extended family spanned several social strata, and she noted with interest the way that her wealthier relations interacted with their poorer kin. Clegg was reminded of gods toying with lesser mortals, and this led to her creation of the Eternals. She also sought inspiration in The Bible, deriving the prize of Enlightenment from the Tree of Knowledge in the Book Of Genesis. Finally, Clegg seized upon the image of solar winds — actually streams of charged particles ejected from the Sun — to develop the premise of the Eternals racing through the solar system.
- The Other Marty:
- Peter Sallis was booked to play Captain Striker, as director Fiona Cumming recalled that he had played a similarly detached character in the 1974 BBC drama The Pallisers. Sallis did attend one day of rehearsal before a strike started and production dates were charged. Sallis was signed up to a Last of the Summer Wine special and so could not make the dates. So, Keith Barron was cast instead.
- David Rhule was originally cast as Mansell, but he also had to drop out, so singer Leee John replaced him at short notice, despite having no previous acting experience.
- Recycled Script: The plot is similar to that of "The War Games": both involve aliens abducting humans from various points in Earth history and using them for their own ends.
- Throw It In!: Believe it or not, the inclusion of Leee John as Mansell wasn't a case of Stunt Casting, at least not intentionally: the actor who was supposed to play Mansell, David Rhule, dropped out at the last minute because of an industrial strike at the BBC that took place just after rehearsals had begun. The last-minute inclusion of John, combined with his lack of prior acting experience, is the reason why his performance throughout the serial is so stiff-yet-excessive.
- So My Kids Can Watch: Barbara Clegg wanted to write for the series to please her children.
- Troubled Production: Much like the previous serial, this one ran into some problems:
- Janet Fielding struggled with the low cut ball-gown she wore during filming, as it threatened to expose her breasts on a number of occasions. At one point, Peter Davison concluded a line with the ad-lib, "Oh, and Tegan, put your boobs back in!" whereupon Fielding realised that she had accidentally exposed herself.
- Mark Strickson was injured while filming the scene of Turlough throwing himself overboard, when the Kirby wire he was suspended from broke, leaving him only able to walk with difficulty for several weeks.
- The electricians union the EEPTU, had begun strike action which disrupted the filming of a number of BBC productions and potentially meaning the final three serials of the season would have to be abandoned. The electricians dispute was settled, but it had badly affected the series recording schedule. The crew were able to shoot the following serial "The King's Demons" on schedule, meaning that there was only one recording block left for the part-completed "Enlightenment" and the planned season finale, "The Return". With some filming already completed, and its importance in concluding the Black Guardian story-arc, it was decided that "Enlightenment" should take precedence and so it had its second production block moved to January 1983, while "The Return" was abandoned.
- Due to the delays, the serial only finished filming around a month before its transmission date, meaning that composer Malcolm Clarke only received the first episode for scoring a week before broadcast, having to rely on musical cues he had recorded weeks earlier without having seen any footage.
- What Could Have Been:
- Working Title: The Enlighteners.
- Write Who You Know: Barbara Clegg based the Eternals on a wealthy group of her relatives, who upon visiting her had demanded constant entertainment, treating other family members almost as "lesser beings"
- You Look Familiar: Tony Caunter (Jackson) had previously played Thatcher and Morgan.
- You Sound Familiar: Lynda Baron had previously sung "The Ballad of the Last Chance Saloon".
Trivia / Doctor Who S20 E5 "Enlightenment"