While Jimmy Fallon is soaking up some Florida sunshine (or moonlight, as the case may be) during his 'Tonight Show' week in Orlando, fun. debuted their brand-new song, 'Harsh Lights' on the show to a packed crowd of pumped fans.

Frontman Nathan Ruess commanded the stage during the performance, strutting in every direction with a gold mic in his hand while rocking a satin letterman jacket and belting out the new track.

"Slipping into midnight, under harsh light / Nothing gets me down," Ruess sings on the chorus, as the rest of the band jams out behind him and the camera pans over the packed audience, who are rocking and swaying to the tune with their hands in the air.

What we love about 'Harsh Lights' is that it's a trademark fun. power ballad, with the driving force of the band's passionate beats and Ruess' distinct falsetto vocals.

Watch fun. debut 'Harsh Lights' in the video above!

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