Emergency lamp: how rechargeable and escape lights work

Two kinds of emergency lamp

The name covers two different products. The first is a portable, rechargeable emergency lamp for homes and shops: it sits on charge, comes on by itself when the power goes, and can be carried around. The second is fixed emergency lighting in a building — wall or ceiling fittings that light the way to the exits when the normal lights fail.

Both work on the same principle. A battery inside the fitting, or a central battery or generator, takes over the moment the mains supply stops.

How a rechargeable emergency light works

Philips describes its rechargeable emergency lights simply: they charge while connected to the power and switch on automatically during a power failure. Most of its models, it says, have overcharge protection, so they can be left plugged in. Its range is mostly portable lamps and lanterns, one of them with a solar panel.

What to check when you choose one

Philips lists the points that separate one model from another:

1. Brightness — enough lumens for the space it must light.
2. Battery backup time — how many hours it runs once the power is off.
3. Recharge time — how quickly it is ready again after use.
4. Mounting — wall, ceiling or carried by hand.
5. Use — indoor, or a model built for outdoor conditions.

Philips builds its emergency lights with LEDs and gives energy efficiency as the reason. For how lumens compare with old bulb wattages, see LED lights.

Emergency lighting in buildings

For workplaces, the UK Health and Safety Executive’s guide Lighting at work (HSG38) separates two types and sets out what each needs:

Emergency lighting in buildings

Point	What HSG38 says
Standby lighting	lets people carry on working; 5% to 100% of normal light, depending on the work
Escape lighting	lets people leave the building safely
Switch-on time	escape lighting should reach its level within 5 seconds of the failure (BS 5266-1); 15 seconds where people know the building
Running time	battery-powered escape lighting is usually designed for one to three hours
Mounting height	at least 2 m above the floor to avoid glare, but not much higher, because smoke may cut the light
Where	emergency exits, escape routes, exit and direction signs, fire alarm points and fire-fighting equipment

HSG38 adds three conditions. The light must last as long as the danger does, or until normal lighting returns; it must give full output at once, which rules out lamp types slow to warm up; and the lighting outside the building must be good enough for people to get clear safely.

The systems range from fittings with their own battery packs to central batteries or a generator feeding the lamps through protected wiring. These are UK figures, given as a reference for how such systems are specified rather than as Tanzanian rules.

Looking after the battery

An emergency lamp that has not been charged is just a lamp. Philips advises keeping the light fully charged so it is ready, checking the battery from time to time, wiping it with a soft cloth and keeping it away from moisture unless the model is waterproof. HSE also lists maintenance — cleaning, repair and replacement — as part of keeping emergency lighting fit for use.