I think the main difference is that a Bright AC often has a deeper playlist. Im not an expert on either format, but I think a Hot AC tends to lean more Rock from the 90s and today, while a bright ac will play both Softer AC titles, some 70s titles, and depending on the station they may play more Non Rap Rhythmic Hits than a Hot AC........ I think the old K-big in LA was basically a bright ac, while Star 98.7 was a hot ac.........Correct me if im wrong.
Actually Star 98.7 used to be a Modern AC like the old Star 95.7 in Tampa Bay, and K-BIG used to be a Rhythmic Hot AC.