Emergency lighting exists so that people can leave a building when the normal lighting fails, which in a fire is exactly when it does. The two main types differ in one respect: whether the emergency lamp is lit all the time or only when the mains fails. That single difference decides where each one belongs.
How does emergency lighting work?
Each luminaire, or a central system serving many, holds a battery kept charged from the mains. When the supply to the local lighting circuit fails, the unit switches to its battery and lights for its rated duration, commonly one or three hours. Crucially the sensing is local: it watches the supply to the lighting in that area, so that a single tripped circuit lights the emergency units in that area rather than needing a whole building failure.
Non maintained
The emergency lamp is off in normal use and lights only when the mains fails. This is the common choice in workplaces, offices, factories and schools, where the normal lighting is on whenever people are present. It uses no energy in normal operation and the lamp life is spent only when it is needed.
Maintained
The lamp is lit continuously, on the mains in normal use and on the battery when the mains fails. It is used where the normal lighting may be deliberately dimmed or switched off while people are present: cinemas, theatres, nightclubs and some assembly buildings. Exit signs are frequently maintained for the same reason, so the sign is legible whether or not the general lighting is on.
Sustained, central battery and where to put them
Sustained luminaires carry two lamps, one mains and one emergency, giving the effect of maintained operation with separate lamps. Central battery systems place one large battery in a plant room serving many luminaires, which simplifies testing and concentrates the risk. Whichever type, the positions are decided by the escape route: changes of direction, stairs, exits, escape route intersections, and the locations of firefighting equipment and call points.
Maintained or non maintained emergency light, decided by the building
The choice is not a preference, it follows from what the building is and how it is used. A maintained fitting is lit whenever the premises are occupied and continues on its battery when the supply fails, and that is what is needed where the public may be present and the normal lighting can be dimmed or switched off: cinemas, theatres, clubs, licensed premises, and exit signs almost everywhere, because a sign nobody can see when the lights are on is no use. A non maintained fitting is off until the supply fails, which suits premises where the occupants know the building and the normal lighting is on whenever anybody is there: offices, factories, workshops, many shops. The practical differences that follow are lamp life and energy in the maintained case, and, on the test regime, the fact that a non maintained fitting gives no daily visual clue that it is alive, which is why its monthly functional test is the one that actually gets skipped.
Questions people ask about maintained and non maintained emergency lighting
What is the difference between maintained and non maintained?
A maintained luminaire is lit all the time; a non maintained one lights only when the mains fails. Maintained is used where the normal lighting may be off while people are present.
Where must emergency lighting be positioned?
At changes of direction and level, at stairs, at exits and escape route intersections, and at firefighting equipment and call points, so the route is usable and the equipment findable.
Should exit signs be maintained?
Frequently yes, so that the sign is legible whether or not the general lighting is on. Whether a particular building needs maintained signs comes out of its design and risk assessment.
When do you use maintained and non maintained emergency lights?
Maintained where the fitting is lit all the time the building is occupied, such as an exit sign people need to see with the power on. Non maintained where it only lights on failure, which is most corridors and stairs.