Battery Saver - Chevrolet 1997 Lumina Owner's Manual

Rearview Mirror Reading Lamps Battery Saver
Your vehcle has
a
feature to help prevent you from
draining the battery, in case you accidentally leave the
courtesy lamps on. If you leave the dial turned all the
way up, or if you leave a door open, the lamps will
automatically turn off after 10 minutes if the ignition
is off.
These lamps go on when you open the doors. When
the doors are closed, turn the lamps on and off with
the switches.