Unfortunately, emergencies happen day or night. Sometimes the people in a building are visitors, unfamiliar with the layout. Often the crisis may cause the electrics to fail, so Emergency Exit Lights have a battery backup to guide people to a safe exit point.
Under AS 2293.1 all Class 6 buildings over 100 m2 require emergency exit lights. They must also be installed on every level of Class 5, 7, 8 or 9 building where any level has a floor area of more than 300 m2. All required emergency lights and exit signs should comply with the standard.