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Don’t worry about their matching choir robes and big smiles: The Polyphonic Spree is not a cult, just an 18-member vocal group that aims to spread happiness. For 13 years, the Spree has created rich chamber pop that serves as a grandiose celebration of all things optimistic. You know the group by its earwormy magnum opus “Light and Day”—that song from Scrubs, last year’s film adaptation of The Lorax, and various commercials. In recent months, the band has been as prolific as it is positive, releasing a Christmas record, a live album of Rocky Horror Picture Show songs, and a new batch of originals on last month’s Yes, It’s True. This new material and a back catalog of psychedelic singalongs (check out the band’s cover of Nirvana’s “Lithium”) could make for a surprising live show. But the cathartic rush of their angelic harmonies and major chords—that should be a given.

The Polyphonic Spree performs at 8 p.m. at Sixth & I Historic Synagogue, 600 I St. NW. $20. (202) 408-3100. sixthandi.org.