The lights that unfortunately come on at the end of the night at the club. This usually alerts the victim that he has spent the last 2 hours talking to a chick that is gross. This surprises the victim who was under the impression that he/she was talking to an attractive girl/guy until the lights came on and made him say... whoa this bitch/dude is ugly. Hence "whoa lights"
Nick: Yo Rob, did you bang that chick I saw you talking to at the club last night?
Rob: Hell no! The whoa lights came on and I realized she had a God Damn wart on her cheek.