Luke Bryan, Katy Perry and Lionel Richie Center Stage in Nashville for 'Idol' Auditions

Luke Bryan has boots on the ground in Nashville looking for the next "American Idol" ... and after holding auditions, he hopped on stage at his own bar with Katy Perry and Lionel Richie.

TMZ obtained video of all 3 'Idol' judges cutting loose Sunday night at Luke's 32 Bridge bar in the heart of downtown Nashville ... and they were having a grand ole time, performing in front of a packed house.

Ya gotta see the video ... Luke's getting the crowd hyped in front of a full band, Lionel's dancing and keeping the beat and Katy's clapping along in an animal print coat.

She also made sure everyone had full drinks. Seriously, it looks super fun!!!

The star-studded trio is in Nashville holding auditions for the 20th season of "American Idol" before it starts airing February on ABC... and we're told they decided to crash Luke's joint once they were off the clock.