The prime use of Emergency Lighting is to help ensure a safe escape in a fire when mains lighting is lost. They may be used to light the escape route, and/or as a beacon of light at the exit that people can aim for in the darkness.
They may also be used as stairwell backup lighting, and as automated convenience lighting for living areas, consumer unit, and so on.
Why Have One?
No-one expects they'll have a fire, but the fact is a lot of people die in the 69,000 house fires every year. Electrical faults, irresponsible tenants, stupid kids, smokers, neighbouring fires, these and more are causes of house fires.
A big problem with fire is smoke. Smoke can totally disorient people, even when they know their own property well. Even trained firefighters quickly become disoriented in dense smoke.
Smoke inhalation is a major killer, more so than burning by fire.
Smoke produced in a fire rapidly and heavily decreases light levels and visibility. In some fires its impossible to see one's own hands due to the smoke density.
With all these factors, escape from a property, while normally elementary, can fail to happen in a fire, with disastrous results.
For under £20 you can give yourself and your family more chance of staying alive.
Maintained & non-maintained
Non-maintained fittings only light when the mains supply fails.
Maintained fittings light when mains lighting fails, but also can be switched on by a light switch for regular daily use.
Sustained fittings behave similarly to maintained fittings, but the internal setup is different. They use 2 separate sets of lights, one for mains use and one for battery use.
Filament & fluorescent
Fluorescent tubes have much longer life than filament lamps, so are less likely to fail. Units with 2 filament lamps improve the odds, but 2 filament lamps still have much shorter life and thus higher failure rate than one fluorescent tube.
Fittings should be tested every so often, as batteries & bulbs don't last forever. Testing should check they work and that they illuminate for the required time period.
To light an escape exit point, lighting high up is needed, as low lights are liable to be obscured from direct view by various objects.
Smoke tends to rise, with clearer air toward the ground. The recommended method of escape in dense smoke is on hands and knees. Smoke may be too dense for light to carry from high up to the ground. For these reasons, mounting lighting low down is more effective when used to light an escape route.
Attention should also be given to lighting access routes, stairways\steps and other obstacles, junctions and also fire fighting equipment such as extinguishers and blankets. Additional lighting is often overlooked in places not on an escape route, such as doorways to and in rooms where people may need to escape from.
These are applied to a light fitting to give an emergency escape symbol. They block most of the light output, making the emergency lighting much less effective.
Legends are applied to lighting to show the route to an exit, as the lighting can be at intermediate points throughout the escape route. If the lighting is insufficient with legends fitted on the front then luminous legends can be fitted near to each emergency light fitting.