This NASA's image of a Mercury-Redstone rocket Freedom 7 carrying Alan Shepard, the first American in space, is titled Light the Candle:
Light the Candle (Image Credit: NASA)
I remember this phrase also mentioned in the movie The Right Stuff, with Alan Shepard (Scott Glenn) waiting for the launch to commence for a rather long time, having to urinate in his suit before launch, because he was sat in his capsule with no easy way to exit it for so long (and the movie portrays many cups of coffee that he had that morning before leaving home, in a somewhat jocular manner) that he couldn't hold it any longer. If I remember correctly from the movie, one of his fellow astronauts in the control center says: "Let's light the candle!", to which control center crew looks at each other and Wernher von Braun agrees: "Yes. Light the candle!". Gustav Holst's Op. 32 "The Planets" starts playing in the background (I believe a passage from act 4, Jupiter, the Bringer of Jollity) and seconds after, the countdown resumes and the the first American manned suborbital spaceflight launches.
Now, that's only a movie and they often dramatize events differently than they really happened, so here's my question:
Who coined the phrase "Light the Candle!" to commence with a rocket launch, and how does the story really go? Did The Right Stuff movie accurately portray events before the Freedom 7 launch, or is there some other story behind this phrase?
Please provide references for claims in your answers.