Originally recorded by Kasey Cisyk (US #80 1977).
Other hit versions by Debby Boone (US #1/CAN #1/UK #48 1977), LeAnn Rimes (US#34/C&W #48 1997).
From the wiki: “Kasey Cisyk’s work singing commercial jingles brought her to the attention of Joe Brooks, who worked as a composer and arranger of jingles. Brooks, who wrote, directed and composed the score for the movie You Light Up My Life chose Cisyk to dub the singing voice of actress Didi Conn.
“Cisyk’s performance of the song appears on the original soundtrack album, and was released as a single, although she was not listed as the performing artist in the final credits of the film (for which she successfully sued the producers). Her single release of the song reached #80 on the Billboard Hot 100 charts.