Target Field has different lighting schemes that are used for specific purposes.
The most highly visible lighting scheme is when the "event lights" are on and used for the playing of night games and/or day games when sun light does not provide the proper illumination of the field.
The other most used lighting scheme is a set of lights called "housekeeping lights" which are used after each night game (and some day games, if necessary) so teams of employees can clean the ballpark seating areas in a safe manner.
It is Minnesota Twins policy to clean the ballpark immediately following a game to reduce the potential of windblown debris and to maintain the facility in a world class fashion. Cleaning immediately after games also ensures the facility is ready for events other than baseball that occur in the building on a daily basis.
Housekeeping lights will remain on for a minimum of 8 hours after the conclusion of a game and likely longer. Nearly 150 people work to clean the facility inside and out and it takes that long to work through the 1 million square feet of space that makes up Target Field.
About two hours after the debris clean up begins, pressure washing is scheduled to start as an eight-hour shift. For example with a typical Sunday first pitch at 1:10 PM game, the Arena Team start at 5:00 pm and the Pressure Wash Team started at 7:00 pm and works until 3:00-3:30 a.m. Because the cleaning service supervisors continue to inspect the work and clean-up puddles after the pressure washing crews finish, there are several crew leaders here until about 4:00 a.m. When all work is completed, crews advise the operations center and the lights are turned off.
Target Field stadium and/or housekeeping lights will also be illuminated on occasion and as necessary for testing and maintenance, but the majority of those occurrences will be during the day.