Emergency lighting is normally required to operate fully automatically and give illumination to a sufficiently high level to enable occupants of all ages to evacuate the premises safely. Most new buildings now have emergency lighting installed during construction.
Non-maintained
The emergency light is only illuminated upon interruption of the mains supply.
Maintained
The emergency light uses the same source for both modes and is usually switched on and in emergency mode.
Sustained
The emergency light has a separate light source for both mains and emergency mode.