Why are stadium lights on?

At least three times recently, while taking the dog out between 5:30-6:00am, the stadium lights have been blazing and creating significant light pollution.

Does anyone know why they are on at that time of day?

Does anyone know the rules and regulations on when the lights can be on? I understand when there is an event but it seems wasteful and unpleasant to pollute the skies needlessly at other times.