Emergency Lighting terms explained

When specifying for any critical back up system, uninterruptible power suppliers, generators, and Emergency Lighting systems, you can be confronted by new terminology – which could be confusing if you’re not familiar with it. Our “Emergency Lighting terms explained” is here to clear any of that confusion.

A’ national deviation – Is a National exception to a European standard it can only be allowed if needed to meet specific site conditions or pre-existing legislation.

Ballast – Is the control circuit which controls the operation of a fluorescent lamp from a specified AC or DC source (typically in the range 2.4–240 V).

Ballast lumen factor (BLF)-Is the ratio of the light output of the lamp when the ballast under test compared with the light output of the same lamp operated with the appropriate reference ballast supplied as its rated voltage and frequency.

Battery – Secondary cells providing the source of power during mains failure.

Battery capacity – The discharge capability of a battery, in ampere hours over a stated duration.

Borrowed light – The assistance in illumination from other sources.

Central battery system – A system in which the emergency batteries for a number of luminaires are housed in one location.

Combined emergency luminaire (previously known as sustained) – Contains two or more lamps one of which is energized from the emergency supply and the remainder from the normal supply. The emergency lamp in a combined emergency luminaire is either maintained or non-maintained.

Competent person – Is someone with the relevant current training and experience, with access to the requisite tools, equipment and information so they are capable of carrying out the required tasks.

Deviation – (term still used in emergency lighting is the same as a variation in fire alarms) If the designer or installer deviates from the requirements of the code of practice they must identify the reasons to demonstrate that the safety of the building is not impaired. All relevant parties must be notified, and the details must be recorded in the log book.

Driver – Is the circuit to control the supply to Light Emitting Diode(led) light sources.

Emergency exit – A way out which is intended to be used any time the premises are occupied.

‘F’ mark – Shows that the luminaire can be mounted on combustible surfaces. It does not show that the luminaire is fire retardant.

Illuminance – Is the luminous flux(light) it is defined as a value in lux (lx) which is the number of lumens per square metre on the surface being illuminated.

Luminaire – Is the technical term for a light fitting it distributes, filters and transforms the lighting provided by lamps.

Maintained emergency luminaires – Illuminate from the normal mains and from the emergency supply.

Mounting height – Is the vertical distance between the luminaire and the working plane, the floor is taken to be the working plane for emergency escape route lighting.

Material time – Is the time when illumination should be provided. It often refers to the time that maintained exit signs need to be illuminated which is when the building is occupied.

Non-maintained emergency luminaire – Contains lamp(s), which only illuminate upon failure of the normal mains supply.

Normal lighting – Is permanently installed lighting operating from the normal electrical supply, that is intended to be used when the premises are occupied.

Place of Safety – Is a safe area beyond the premises where occupants are no longer at risk.

Rated duration – Is the manufacturer’s declared duration, specifying the time for which the emergency lighting will provide the rated lumen output after mains failure.

Re-charge period – Is the time for the batteries to regain sufficient capacity to achieve their rated duration.

Self-contained emergency luminaire or single-point luminaire – Is a luminaire or sign providing maintained or non-maintained emergency lighting in which the components such as battery, lamp, and the control unit are contained within the housing or within one metre.

(Slave) or Centrally Supplied luminaire – Is an emergency luminaire without its own batteries designed to work with a central battery system or generator.

850°C glow wire test – Is required by BS 60598-2-22 for luminaire housings to protect the installation so that battery or internal circuit faults will not set fire to the luminaire.


Ian Watts was co-opted onto the committee responsible for the drafting of BS.5266 part 1 in 2015, as the independent industry expert on new technology. As Business Development Manager for KOHLER Uninterruptible Power he has contributed to the drafting of BS.7273 part 6, a draft standard currently out for public comment to look at fire interface devices including the integration of dynamic emergency lighting systems. Sitting on the CEN 169 working group 3, tasked with this same development provides him with a European insight into this exciting market. He lectures for CIBSE and has been a trainer for the FIA since 2012.

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