My Songs Know What You Did in the Dark (Light 'Em Up) is a song composed by Americanpop punk group Fall out Boy released on February 4, 2013, in the United States. The single marks the band's comeback four years of being on an indefinite hiatus in 2009. The band announced that "Light 'Em Up" is the lead single from the fifth studio albumSave Rock and Roll, which was released on April 12, 2013.
Commercially, "My Songs Know What You Did in the Dark (Light 'Em Up)" debuted on charts worldwide with modest success, debuting in the top five in the United Kingdom and at No. 36 on the Australian ARIA Chart, charts the band have previously received success from with singles like "This Ain't a Scene, It's an Arms Race" and "Thnks fr th Mmrs". On the Billboard Hot 100, the song debuted at No. 26 and No. 8 on US Rock Songs; it reached No. 2 on iTunes upon its release. Fall Out Boy performed the song on Jimmy Kimmel Live! for their first post-hiatus TV performance on February 13.