First Came The Film, Then The Song
I see much bad trivia being passed on this board regarding the legitimacy of this film. Contrary to comments posted here, the film came first. Not that it is a good film. But you have to consider that the Academy's music branch never would've awarded the song the Oscar if it were not an original song written for a film--instead of a film written to promote a song that was already rising in the charts, as some posters have suggested. Case in point: Amanda McBroom's song The Rose which featured in the film of the same name two years later won a Golden Globe for Best Song but was not eligible for an Oscar because McBroom had actually composed and recorded it for herself prior to lending it to the film--it was therefore not an original song written for the film. Composer Joe Brooks would've surely suffered the same fate had his song (You Light Up My Life) not have been legitimately written for his film (which he also wrote and directed). Brooks may not have been much of either but the song he wrote for the film obviously struck a chord (with some people).
You Light Up My Life was not rushed into production to promote the already released Debby Boone record. In fact, the song was already recorded by a session singer named Kacey Cisyk whose version appears in the film and on the OST. Ms. Cisyk--who received some publicity after Debby Boone had a hit with it--didn't think much of the song and didn't see any future in it. She didn't wish to be associated with it as a recording artist. Hence, Brooks combed the Warner Bros. catalog for a sound alike singer and came up with Debby Boone. Her version, released to coincide with the release of the film, was a little bit of a sleeper at first but then rapidly climbed up the charts. Apparently, Arista Records then tried to release Cisyk's version as a single to compete with Boone's version but it went nowhere. Cisyk was a trained opera singer which might've had something to do with her initial hesitation. She died of breast cancer in 1998.