What is emergency lighting?
Emergency lighting is lighting that operates automatically when the normal supply fails, illuminating escape routes and exits for long enough to let people leave the building safely.
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<img src="https://fireoptix.co.uk/glossary/emergency-lighting/diagram.svg" alt="emergency lighting — diagram from FireOptix" width="880" height="620" loading="lazy">
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<a href="https://fireoptix.co.uk/glossary/emergency-lighting">What is emergency lighting?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
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</figure>It exists for the case where a fire takes the power with it. A route that is obvious in normal light can be impossible to follow in darkness and smoke, and the lighting is what keeps the exit signs and the floor visible.
Its failure mode is silent. A battery degrades without any outward sign, so the only way to know the system works is to test it — briefly and often for function, and for its full rated duration much less frequently.
The record of those tests is the evidence. A system that works but has no test history is indistinguishable, to an inspector, from one that has never been checked.
In practice
A building where only the short function test has ever been run.
Every fitting switches on when tested. Nobody has ever established that any of them stays on for the period the system was designed for.
The two tests prove different things, and a log with one column cannot tell you which was done.
A building can have a perfect test record and emergency lighting that fails within minutes of a real outage.
What goes wrong in practice
- Function tests carried out but never written down, leaving no evidence they happened.
- A failed luminaire noted during a test and not raised as a defect with an owner.
- New partitions or shelving installed after commissioning, putting parts of the route into shadow.