Planning Emergency Lighting: A Step-by-Step Design Guide

What does emergency lighting design start with?

Emergency lighting design is the process of deciding where safety luminaires and exit signs are installed, and with which power supply, so that people can leave a building safely when the normal supply fails. It does not start with choosing products but with three documents:

• Fire safety strategy or building permit: for buildings requiring approval and for high-risk buildings, it states whether emergency lighting is required, which areas it must cover and often the rated duration.
• Risk assessment: in workplaces, the employer assesses whether people are at risk if the normal lighting fails. National rules define the details – in Germany, for example, workplace rules ASR A2.3 and ASR A3.4.
• Escape route plan or floor plans: showing escape routes, exits, stairwells and safety equipment.

Whether lighting is required at all is covered in When is emergency lighting required?. In existing buildings the actual situation on site matters too: alterations, furniture and changes of use often differ from the drawings. NOTLUX therefore starts every project with an on-site survey that records escape routes, existing luminaires and mounting options.

Defining escape routes and points of emphasis

The first design step is to mark the areas that must be lit: escape routes, open areas (larger spaces without defined routes, see Anti-panic lighting) and high-risk task areas. Then the locations are marked where EN 1838 and EN 50172 require a luminaire nearby. "Nearby" generally means within 2 m measured horizontally.

• at every exit door intended for emergency use, and outside near each final exit,
• at every change of direction and every intersection of corridors,
• near stairs, so that each tread receives direct light,
• near any other change of floor level, such as ramps or single steps,
• at exit signs that must be illuminated,
• at fire extinguishers, hose reels, manual call points and first aid points (at least 5 lx vertical there),
• at emergency call devices and areas for people with disabilities, such as accessible toilets.

These points of emphasis form the framework. Only then is it checked whether the spacing between them achieves the required illuminance or whether additional luminaires are needed.

Which power supply system fits?

Before calculating, the system is chosen: self-contained, low power supply (LPS) or central battery (CPS). The choice affects luminaire selection, cabling, space requirements and testing effort. Self-contained luminaires need no separate safety power distribution and suit small to medium buildings and retrofits; central systems offer central monitoring but usually require fire-resistant cabling and a suitable plant room. The full comparison is in Self-contained vs central battery.

At the same time the rated duration is fixed – how long the system must operate in emergency mode: at least 1 hour, and 3 hours for many building types depending on national rules. It also has to be clarified which exit signs must be maintained (lit permanently, including during normal operation).

Photometric calculation with LDT data

Illuminance is verified by photometric calculation. The basis is the LDT file (EULUMDAT format), which stores a luminaire's luminous intensity distribution. Software such as DIALux or Relux uses it to calculate floor-level illuminance in emergency mode. The target values of EN 1838:

A robust calculation follows a few rules:

• Use the emergency luminous flux: calculate with the flux in emergency mode, not mains operation. With emergency drivers it is often considerably lower.
• Ignore reflections: the standard counts direct light only; reflections from walls and ceiling are disregarded.
• Worst case: values must be met at the end of the rated duration and throughout service life, so a maintenance factor applies.
• Mounting height: EN 1838 requires luminaires to be mounted at least 2 m above floor level.

Values and uniformity are explained in Emergency lighting illuminance.

Manufacturer spacing tables

For straight corridors and standard rooms, the manufacturer's spacing tables are often sufficient. For each optic and mounting height they state the maximum distance between luminaires and from walls to achieve 1 lx on the centre line or 0.5 lx across an open area. A wide corridor lens (around 135 × 55°) allows greater spacing along an escape route than a rotationally symmetrical optic, which is better suited to open areas.

Exit signs and viewing distance

Exit signs are planned alongside the lighting. From every point on an escape route at least one sign leading to the nearest exit must be visible. The permissible distance follows from the viewing distance in EN 1838: d = z × h, pictogram height times distance factor (z = 200 for internally illuminated, z = 100 for externally illuminated signs). An internally illuminated sign with a 15 cm pictogram therefore covers up to 30 m. See Exit sign viewing distance and, for signage as a whole, Escape route signage.

Documentation and handover

A design is only complete with full documentation. EN 50172 requires records to be available when the system is handed over to the operator. These typically include:

• floor plans showing escape routes, all luminaires and exit signs, with unique luminaire numbering,
• the photometric calculation or proof of spacing,
• details of system type, rated duration, mode of operation and circuits,
• the installer's completion certificate and commissioning test report,
• operating and maintenance instructions for the components,
• the logbook, prepared for periodic testing.

In high-risk buildings, many countries require an inspection by an approved expert before commissioning, who will review exactly these documents.

Common design mistakes

• Drawings instead of reality: designing from old floor plans although walls have moved or rooms changed use.
• Mains flux instead of emergency flux in the calculation, overstating illuminance in emergency mode.
• Missed points of emphasis, especially level changes, extinguishers away from corridors and the area outside the final exit.
• Externally illuminated signs calculated as internally illuminated, halving the real viewing distance.
• Ignored obstructions: shelving, acoustic panels or door leaves hiding luminaires and signs.
• Rated duration not clarified, for example 1 h planned where the fire strategy requires 3 h.
• Testability forgotten: luminaires mounted high without access make every monthly test harder; self-testing luminaires to EN 62034 reduce this effort.