"You Light Up My Life" is a ballad written by Joseph Brooks. The best-known cover version of the song was a cover by Debby Boone, the daughter of singer Pat Boone. It held the No. 1 position on the Billboard Hot 100 chart for ten consecutive weeks in 1977 and topped Record World magazine's Top 100 Singles Chart for a record 13 weeks.

The single was an enormous success. It became the biggest single of the 1970s in the United States, setting a new Billboard Hot 100 record for most weeks spent at Number One.
~Source: Wikipedia