Emergency Lighting to BS 5266: Durations, Coverage & Common Mistakes

Emergency lighting isn't ordinary lighting with a battery — it's a life-safety system with its own standard, BS 5266 (with the illuminance criteria in BS EN 1838), and it's where lighting designs most often come unstuck at building control. Here's what it actually has to achieve, the numbers that matter, and the mistakes that get designs sent back.

The short version: emergency lighting is judged on the illuminance on the floor and on covering the right places (exits, stairs, safety equipment) — not on a fitting spacing. Get the duration right for the building use, calculate it on the real layout, and put a luminaire at every point of emphasis.

What Emergency Lighting Has to Do

When the normal supply fails, the emergency lighting has to let people leave safely and find the safety equipment on the way out. That breaks into three jobs: light the escape routes, provide open-area (anti-panic) light so people can reach a route, and cover high-risk task areas where a sudden loss of light would be dangerous. Each has its own illuminance target, and each is a separate calculation.

The Illuminance Targets

Area	Minimum illuminance	Note
Escape route centre line (≤ 2 m wide)	1 lux	Central band (half width) ≥ 0.5 lux
Open / anti-panic area	0.5 lux	Excludes a 0.5 m border
High-risk task area	10% of maintained, ≥ 15 lux	Essentially immediate

Plus: uniformity along an escape route no worse than 40:1 (max:min), and timing of at least 50% of the level within 5 seconds and 100% within 60 seconds of failure.

Durations: One Hour or Three?

The system has to run on its own power for a defined duration. Three hours is usual where people sleep on the premises, where the building is used by the public, or where it won't be re-occupied immediately. One hour can be acceptable where the premises are evacuated at once on failure and not re-occupied until the batteries have recharged. The occupancy drives the choice — get it wrong and the whole system is the wrong size, because duration sets the battery and therefore the cost and the maintenance burden.

Coverage Is About the Floor, Not the Fitting

The requirement is a minimum illuminance on the ground, not a fitting every so many metres. Just as important are the points of emphasis that must have a luminaire near them:

Every exit door and final exit
Stairs and every change of floor level
Changes of direction along an escape route
Fire-alarm call points and firefighting equipment
First-aid points
Lifts, escalators and disabled refuges / emergency communication points

Maintained or Non-Maintained, Self-Contained or Central

Maintained fittings are lit all the time (common in public spaces); non-maintained only come on when the mains fails. Power is either self-contained (a battery in each fitting) or from a central battery system. Each has cost, maintenance and fire-survival implications — a central system, for instance, brings the supply cabling into scope for fire-rated support (see BS 8519 supports), because the cable feeding the luminaires must itself survive the fire.

Testing Is Part of the Design

BS 5266 expects a monthly function test (each luminaire switches to emergency and its lamp works) and an annual full-duration test (the batteries hold the full 1 or 3 hours), all logged. Designing in self-test or addressable luminaires makes that routine automatic and auditable — worth specifying on any building where a facilities team will otherwise be walking round with a key switch and a stopwatch.

Where Designs Go Wrong

Spacing fittings from a manufacturer table instead of calculating illuminance on the actual layout.
Missing points of emphasis — exits and stairs with no dedicated luminaire.
Choosing the wrong duration for the occupancy.
Using the luminaire's rated output rather than its reduced output at the end of the rated duration.
Ignoring uniformity, so the route has bright pools and dark gaps.
Forgetting external illumination to a place of safety beyond the final exit.

What This Means for Your Design

A proper emergency lighting design is a calculation on the real geometry, not a spacing rule of thumb. Our DIALux lighting design service produces emergency illuminance calculations and coverage checks to BS 5266, with the points of emphasis marked up — ready for building control and the fire strategy.

Frequently Asked Questions

How much light does an emergency escape route need?

To BS EN 1838, an escape route up to 2 m wide needs at least 1 lux along the centre line, with a central band (half the route width) at 0.5 lux or more. Wider routes are treated as a series of 2 m strips or as an open area.

When is 3-hour duration required instead of 1 hour?

Three hours is usual where people sleep on the premises, where the building is used by the public, or where it will not be re-occupied immediately. One hour can be acceptable where the premises are evacuated at once on failure and not re-occupied until the batteries have recharged. The building use drives the choice.

What is the difference between maintained and non-maintained?

Maintained emergency luminaires are lit all the time (common in public assembly areas); non-maintained luminaires only illuminate when the normal supply fails. Many fittings are switchable/combined. It is a duty choice, not a quality difference.

How fast must emergency lighting come on?

BS 5266 / BS EN 1838 expect at least 50% of the required illuminance within 5 seconds and the full level within 60 seconds of the normal supply failing (high-risk task areas require essentially immediate response).

What testing does emergency lighting need?

A short monthly function test (to confirm each luminaire switches to emergency and its lamp works) and an annual full-rated-duration test (to confirm the batteries hold up for the full 1 or 3 hours), with the results logged. Automatic self-test luminaires can do much of this and record it.