What song spent the most weeks at number 1 in the '70s?

The answer is: Debby Boone's "You Light Up My Life"

In 1977, Debby Boone's "You Light Up My Life" planted itself at number one and stayed there for 10 straight weeks, crushing every other song that decade. The track started life as a simple tune for the film of the same name, but things got interesting when producer Joe Brooks decided to swap out original singer Kasey Cisyk for Pat Boone's daughter Debby.

Arista Records released the original soundtrack album featuring Cisyk's recording under the anonymous credit "Original Cast." It actually charted on Billboard, reaching #80, while Boone's version rocketed up to the top of both the pop and adult contemporary Billboard charts while cracking the top give in country. People couldn't get enough of what they thought was a romantic love song, though Boone herself was singing it about her relationship with God.

The song's success landed Boone a Grammy for Best New Artist and an American Music Award for Favorite Pop Single. It even scored platinum certification, which was no small feat in the '70s. In 2008, Billboard ranked it as the seventh biggest hit in Hot 100 history.

Not that any of this helped Boone's long-term career. Despite recording four more albums, she never cracked the Top 40 again. But for those 10 weeks in 1977, she outshone the Bee Gees, Andy Gibb, and Wings to claim the longest-running number one of the decade.