Background: Deborah Anne "Debby" Boone (born September 22, 1956), is an American singer, author, and actress. She is best known for her 1977 hit, "You Light Up My Life", which spent ten weeks at No. 1 on the Billboard Hot 100 chart and led to her winning the Grammy Award for Best New Artist the following year. Boone later focused her music career on country music resulting in the 1980 No. 1 country hit "Are You on the Road to Lovin' Me Again". In the 1980s, she recorded Christian music which garnered her four top 10 Contemporary Christian albums as well as two more Grammys.
Context: With her older sisters married and younger sister Laury in college, Boone was actively encouraged by producer Mike Curb to launch a solo career. Boone released her first solo effort, "You Light Up My Life" (which had been featured in the film of the same name) in 1977. The song became the biggest hit of the 1970s spending ten consecutive weeks at No. 1 on the Billboard Hot 100 -- longer than any other song in Hot 100 history to that point. (In 2008, Billboard ranked the song No. 7 among all songs that charted in the 50-year history of the Hot 100.) The song earned Boone a Grammy Award for Best New Artist and an American Music Award for Favorite Pop Single of 1977. She also received Grammy nominations for Best Pop Vocal Performance - Female and Record of the Year won by, respectively, Barbra Streisand ("Love Theme From "A Star Is Born" (Evergreen)") and the Eagles ("Hotel California"). "You Light Up My Life" also succeeded on Billboard's Adult Contemporary (No. 1 for one week) and Country (No. 4) singles charts. The single and the album (No. 6 Pop, No. 6 Country) of the same name were both certified platinum.  The song, written and produced by Joe Brooks, was from the film of the same name. Brooks earned Song of the Year awards at both the 1978 Grammys and Oscars for writing the song. (Boone performed the song at both awards shows.) Boone's version was not used in the movie or featured on its soundtrack. The song was lip-synched in the film by its star, Didi Conn, performing to vocals recorded by Kacey Cisyk. It was written as a love song, but Boone interpreted the song as inspirational and stated that she recorded the song for God.  Boone's overnight success led to a tour with her father and frequent television appearances, but she was unable to maintain her success in pop music after "You Light Up My Life". Her follow-up single, "California" (also written and produced by Joe Brooks), peaked at No. 50 Pop and No. 20 AC. "California" was included on Boone's second album, Midstream, which faltered at No. 147 Pop. Her next single, the double-sided "God Knows"/"Baby I'm Yours", also struggled, peaking at No. 74 Pop, becoming her last entry on the Hot 100. However, the single charted AC (No. 14) and returned Boone to the country chart (No. 22). Boone then released another movie theme, "When You're Loved", from The Magic of Lassie. Like "You Light Up My Life", the song was nominated for an Academy Award for its composers, the Sherman Brothers, but it failed to replicate the success of her first single charting only No. 48 AC. Boone's wholesome persona contrasted with the image-conscious pop-music industry, leading her career in different musical directions.
Question: what was "you light up my life"?

Answer:
The song became the biggest hit of the 1970s