Based on the story by James E. Gunn, originally published in Galaxy Science Fiction, February 1955.
Originally broadcast on NBC, February 1, 1956.
(An article by James E. Gunn, "Space Opera Revisited," appeared in Thrilling Wonder Stories, Volume 1.)
I think this is my favorite X Minus One so far. I wonder how the adapter (Ernest Kinoy, according to Wikipedia; the credit is cut off on the file) got the idea to do it in the form of a non-fiction radio program in the process of assembly. The original story is written in a straightforward way. Kinoy could have done the script as typical X Minus One narration-and-dramatization, but the method he chose worked out much better for the material. Which, I suppose, just goes to show (as some critics have been moved to observe about the Watchmen film) that the best adaptation of a work to a new medium isn't necessarily the most "faithful."
Also according to Wikipedia, "The Cave of Night" was adapted for television's Desilu Playhouse in 1959. A more well-known adaptation is the 1969 TV movie and subsequent series The Immortal, rather loosely based on his 1964 novel The Immortals.
Speaking of Gunn, adaptation, and Desilu, Gunn adapted an unproduced Star Trek storyline by Theodore Sturgeon into the 1996 novel The Joy Machine, credited to both authors.
James E. Gunn is the only writer so far to produce new material for both the original run of Thrilling Wonder Stories and the revival. He wrote an article for Volume 1, as mentioned above, and for the original, co-wrote a short story, wrote another solo, and featured in the final issue with the novella "Name Your Pleasure," which became the last third of his 1961 novel The Joy Makers. (The middle third, "The Naked Sky," appeared in the final issue of what by then was called Startling Stories Combined with Thrilling Wonder and Fantastic Story, but we won't blame him for, in essence, closing out Thrilling Wonder Stories twice.)
He's edited six volumes so far of The Road to Science Fiction, which trace the development of the genre all of the way from the Epic of Gilgamesh with excerpts, full stories, and short essays. My father bought the second and third volumes at a used book sale once, and I learned a lot about the history of science fiction from them. So you have that partially to blame for the existence of this website today.