"You Light Up My Life" is a ballad written by Joe Brooks, and originally recorded by Kasey Cisyk for the soundtrack to the film of the same name.The song was lip synched in the film by its lead, Didi Conn. Later, Debby Boone, Pat Boone's daughter, recorded the single, which became an enormous success, topping the Billboard Hot 100 chart for a (then) record-setting ten consecutive weeks. It became the most successful single of the 1970s in the United States, and set a new Hot 100 record for longest reign at No. 1. (Elvis Presley's double-sided "Don't Be Cruel/Hound Dog", then recognized as the longest-running No. 1 of the rock era, spent eleven weeks atop the Billboard Best Sellers chart in 1956, before the debut of the Hot 100.) The record was matched in 1982 by Olivia Newton-John's "Physical", but never surpassed until a 1991 change in chart methodology allowed songs to achieve longer reigns at No.1 ("End of the Road" by Boyz II Men set the new record, thirteen weeks). The single, which was certified platinum by the Recording Industry Association of America (RIAA), also hit #1 on the Adult Contemporary chart and reached #4 on the Country chart. The single peaked at #48 in the UK Singles Chart.