Emergency Lights

What is an Emergency Light

An emergency light is a luminaire that provides illumination automatically when the normal mains lighting supply fails. Its purpose is not general illumination but safe evacuation: it lets occupants find and follow an escape route, see hazards along the way, and reach an exit without the building lighting they normally rely on. Because it is a life-safety device, its design is governed by mandatory standards rather than by aesthetic or energy preference, and a luminaire that looks identical to a decorative fitting may legally be useless if its battery, changeover time, or light distribution does not meet the relevant code.

Standards split emergency lighting into two broad functions. Emergency escape lighting is the part that enables safe exit, and it subdivides into escape-route lighting (the illuminated path to an exit), open-area or anti-panic lighting (light across a large floor so occupants can reach a route), and high-risk task-area lighting (light that lets a dangerous process be shut down safely). Standby lighting is a separate function that keeps normal activities running during an outage and is not a life-safety requirement, although the same hardware often serves both. EN 1838 defines these functions in Europe; NFPA 101 frames the equivalent United States requirement as means-of-egress illumination.

The history of the category follows the electrification of buildings. Early statutory emergency lighting in the mid twentieth century used tungsten lamps fed by large central lead-acid battery rooms, switched in by relays. From the 1970s, self-contained fluorescent fittings with integral nickel-cadmium batteries made distributed emergency lighting affordable for ordinary buildings. The decisive modern shift is the LED light source, which cut the lamp load by roughly an order of magnitude, so a small lithium or nickel cell can now hold the rated light level for the full 1 to 3 hour duration. The second modern shift is digital addressing: luminaires that test themselves and report status over a DALI bus, removing the manual log-book inspection that historically defeated compliance.

Five performance metrics determine whether an emergency light is fit for purpose: the illuminance it puts on the floor, the rated duration it can hold that level, the changeover (response) time after mains failure, the test regime it supports, and the durability of its battery and enclosure in the installed environment. These five drive the total cost of ownership. A cheap fitting with a short-lived battery and no self-test looks economical at purchase, but the recurring labour of manual annual duration tests and frequent battery swaps across hundreds of fittings usually dwarfs the original price difference within the building's life.

The scale of the category is large because emergency lighting is effectively universal in occupied non-domestic buildings. Almost every office, factory, school, hospital, retail unit, car park, and transport hub in the developed world is legally required to install and maintain it, and the requirement is enforced by fire authorities and insurers. This makes emergency lighting a high-volume, standards-driven, audited product class where conformity documentation matters as much as photometric performance. It is one element of a building's wider life-safety system, working alongside the smoke detectors and the fire doors that detect a fire and contain it while occupants follow the illuminated escape route to an exit.

Luminaire Types and Operating Modes

Emergency luminaires are classified by their operating mode, which describes how they behave relative to the normal lighting, and by their function, which describes what part of the escape system they serve. IEC 60598-2-22 defines the operating modes that appear as a label on every certified fitting. Choosing the wrong mode is a common error: a non-maintained light placed where the general lighting is normally dimmed, such as a theatre, leaves the audience in darkness even when mains power is healthy.

Non-maintained luminaires stay dark while the mains is healthy and only light when the supply fails. They are the default in workplaces and back-of-house areas where the general lighting is already on during occupation, so the emergency fitting adds no value until a failure. The battery is held on charge continuously and the lamp life is preserved because it only runs during tests and real events. The label notation in IEC 60598-2-22 is mode 0.

Maintained luminaires are lit continuously and simply switch their supply from mains to battery on failure, so the light never goes out. They are mandatory for illuminated exit signs, which must be readable at all times, and for places of assembly such as cinemas, theatres, and lecture halls where the general lighting is deliberately dimmed during use and occupants would otherwise be in the dark. The notation is mode 1. Combined and sustained fittings package both behaviours in one housing, with a separate always-on lamp and a battery-backed emergency lamp.

By function, escape-route luminaires are positioned to illuminate the defined path: at each exit door, near stairs and changes of level, at corridor intersections and direction changes, near each fire-fighting device and the fire-alarm manual call point, and outside the final exit. Open-area (anti-panic) luminaires light large floor plates so occupants can see across the space and reach a route, which matters in halls, open-plan offices, and undefined-route spaces above a threshold floor area. High-risk task luminaires light a process that must be made safe before evacuation, for example a press or a furnace. Illuminated exit signs are a distinct subclass governed by both the luminaire standard and the safety-sign standards ISO 3864 and ISO 7010, covered in Chapter 4.

A further distinction is internally illuminated versus externally illuminated exit signs. An internally illuminated sign is backlit by its own LED source and is legible at up to 200 times its pictogram height. An externally illuminated sign relies on a separate light shining on its face and reaches only 100 times its height, so it needs a guaranteed emergency light nearby. Photoluminescent signs, which absorb ambient light and glow in the dark, are accepted under UL 924 in the United States only when they receive a continuous charging illuminance of roughly 54 lux (5 footcandles) at the face during occupancy; they carry no battery and so suit specific low-traffic egress paths rather than primary exits.

Power Architecture and Battery Technology

The power architecture decides where the emergency energy is stored and how it reaches the lamps. There are three mainstream approaches: self-contained luminaires with an integral battery, a central battery system feeding many luminaires from one cabinet, and a central static inverter that produces a mains-like output for the existing fittings. Each has a distinct cost, maintenance, and resilience profile, and the right choice depends on building size and criticality rather than on price alone.

Self-contained luminaires hold the battery, charger, changeover electronics, and lamp inside the fitting. Each unit is autonomous, so wiring is simple, a single failure affects only one light, and zones are easy to extend. The cost is the maintenance burden of many small batteries scattered across the building, each of which ages and must eventually be replaced, and each of which sits in whatever local temperature the ceiling void imposes. Self-contained units dominate offices, schools, and retail. Central battery systems place all the batteries, usually valve-regulated lead-acid or increasingly lithium, in one cabinet that feeds every luminaire over fire-survival cable rated to keep working through a fire. This keeps the batteries in one accessible, temperature-controlled room with central monitoring, which suits hospitals, airports, and high-rise blocks, at the price of higher install cost and the fire-rated cabling. Central static inverters, closely related to an industrial UPS, instead synthesise a mains-quality output on supply failure so the building's normal LED fittings keep working as emergency lights; they are attractive for retrofits but concentrate the risk in a single unit and must transfer within the code response time.

Battery chemistry is the single most consequential reliability decision because the battery, not the LED, is the wear-out item. Four chemistries are in service, and the correct choice is governed by the temperature near the fitting, which is frequently 10 to 15 degrees Celsius hotter than the room air. The table below compares them on the properties that drive emergency-lighting service life.

Nickel-cadmium has long been the workhorse of self-contained emergency lighting because it tolerates the continuous trickle charge and elevated temperatures found at ceiling level, with a typical service life around 4 years and operation up to roughly 55 degrees Celsius. Its drawbacks are a high self-discharge rate, a memory effect, and the cadmium content that has driven restrictions in several markets. Nickel-metal-hydride offers roughly twice the capacity of NiCd in the same physical size and avoids cadmium, but it endures fewer charge cycles and a lower temperature ceiling near 50 degrees Celsius. Lithium iron phosphate has become the preferred chemistry in new self-contained designs: its self-discharge is only 3 to 5 percent per month, it tolerates ambient temperatures up to about 60 degrees Celsius, and its 8 to 10 year service life roughly halves the lifetime cost of battery replacement labour across a large estate. Valve-regulated lead-acid remains the chemistry of central battery cabinets where weight is acceptable and the temperature-controlled room keeps it near its ideal 25 degrees Celsius. Whatever the chemistry, the charging circuit must hold the battery ready without overcharging, and a fault in the charge electronics is a leading cause of premature battery death.

Illuminance, Duration, and Exit Signage Rules

The performance an emergency light must deliver is set by the building code, not by the manufacturer, and the two dominant regimes are the European EN 1838 family and the North American NFPA 101 and International Building Code family. The numbers differ in detail but agree on the principle: a defined minimum light level on the escape path, held for a defined minimum time, struck within a few seconds of failure. Specifying to one regime does not automatically satisfy the other, so a building's location and its authority having jurisdiction decide which set applies.

Under EN 1838, escape-route lighting must provide at least 1 lux along the centre line of a route up to 2 metres wide, measured at floor level, with the central band kept above 0.5 lux. Open-area (anti-panic) lighting must give at least 0.5 lux across the core of the floor, excluding a 0.5 metre border. Points where fire-fighting equipment, the fire alarm call points, or first-aid stations sit must reach at least 5 lux. High-risk task areas must reach 10 percent of the normal task illuminance or at least 15 lux, whichever is greater, struck within 0.5 seconds. To prevent dazzle and dark patches, the ratio of maximum to minimum illuminance along an escape route must not exceed 40:1. The light level must reach 50 percent within 5 seconds and the full required value within 60 seconds of mains failure.

Under NFPA 101, the means-of-egress floor must receive an initial average of at least 10.8 lux (1 footcandle) with no single point below 1.08 lux (0.1 footcandle), again limited to a 40:1 maximum-to-minimum ratio. Because the battery sags over the run time, the code permits the average to decline to no less than about 6.5 lux (0.6 footcandle) at the end of the rated period. Emergency power must reach the luminaires within 10 seconds of normal-supply loss, a limit also stated in NEC Article 700 for emergency systems.

Duration, the rated time the light must hold its level, is the parameter most often dictated by occupancy. The table below summarises the mainstream rules. The rated duration is also exactly the time the annual full-discharge test must prove, so it directly sizes the battery.

Illuminated exit signs are a distinct discipline governed by the same ISO 3864 and ISO 7010 safety-sign standards that define industrial warning signs, applied here alongside the luminaire standard. The pictogram must be the ISO 7010 running figure (symbols E001 and E002) with a directional arrow, in safety green and white. The maximum viewing distance is the pictogram panel height multiplied by 200 for internally illuminated (backlit) signs and by 100 for externally illuminated signs, so a 150 mm internally lit panel is legible at up to 30 metres while the same externally lit panel reaches only 15 metres. EN 1838 sets the sign luminance at a minimum of 2 candela per square metre in the green and white, a maximum-to-minimum luminance ratio of 10:1 within either colour, and a green-to-white luminance ratio between 5:1 and 15:1 so the symbol stays legible without glare. NFPA 101 takes a different route, specifying a 152 mm (6 inch) minimum letter height for word-legend signs and a rated viewing distance of about 30.5 metres (100 feet), which is why United States exit signs use the word EXIT rather than a pictogram.

Key Specification Parameters

Reading an emergency-luminaire data sheet means separating the few parameters that decide compliance from the many that describe the housing. Eight parameters truly drive selection: operating mode, rated duration, light output and distribution, changeover (response) time, battery chemistry, ingress protection, test capability, and conformity marks. Each is explained below.

Operating mode is the IEC 60598-2-22 class covered in Chapter 2: non-maintained (mode 0), maintained (mode 1), combined, or sustained. It must match how the general lighting behaves in the space, because a non-maintained light is useless where the normal lighting is dimmed during occupation. Rated duration is the time the luminaire holds its required light level on battery, stated as 1 h, 2 h, or 3 h. It is set by the building code and occupancy, not chosen for convenience, and it is precisely the value the annual duration test must verify.

Light output and distribution matter more than a single lumen figure. Emergency luminaires are rated by the spacing tables or photometric files that show how far apart they can sit while still meeting the 1 lux escape-route or 0.5 lux open-area minimum at floor level. A high lumen number with a narrow beam can cover less escape route than a lower-lumen wide-distribution optic, so designers work from the manufacturer's spacing data, not the lamp rating. Changeover (response) time is how quickly the luminaire reaches its rated output after mains failure: EN 1838 requires 50 percent within 5 seconds and full output within 60 seconds, while NFPA 101 and NEC 700 require transfer within 10 seconds. High-risk task fittings must respond within 0.5 seconds.

Battery chemistry and rated life determine the replacement interval and the temperature ceiling, as set out in Chapter 3. The data sheet should state the chemistry, the design life in years, and the maximum ambient temperature for the rated life, because mounting a NiCd-rated fitting in a hot ceiling void shortens its battery dramatically. Ingress protection follows the IEC 60529 IP code: IP20 indoors in clean dry areas, IP65 for car parks, external escape routes, and washdown areas (dust-tight and protected against water jets), and IP66 or IP67 where heavy washdown or temporary flooding occurs. Hazardous areas additionally require ATEX and IECEx Ex certification to the IEC 60079 series, the same family of marks carried by general-purpose explosion-proof lighting.

Test capability ranges from manual (a test key and a paper log) through self-test (the fitting runs its own monthly and annual tests on an internal clock and flashes a fault LED) to addressable DALI device type 1 per IEC 62386-202, where a central controller schedules, staggers, and logs every test for the inspection record. The five mainstream output and control interfaces are:

• Manual test key: lowest cost, but compliance depends on staff walking the building and keeping a log book.
• Self-test (autonomous): the fitting tests itself to stored settings and signals faults locally; no wiring beyond the supply.
• DALI emergency (IEC 62386-202): addressable two-wire bus, central scheduling and per-fitting pass/fail logging, staggered tests so routes are never all dark.
• Wireless / radio self-test: battery-status and test reporting over a proprietary or open RF mesh, used for retrofit where bus cabling is impractical.
• Central battery monitoring: the cabinet supervises circuit and battery health for all fed luminaires from one panel.

Conformity marks are not optional paperwork; they are the legal basis for using the fitting. In Europe and much of Asia the luminaire must meet EN 60598-2-22 (IEC 60598-2-22) with performance to EN 1838 and system rules to EN 50172. In North America it must be UL 924 listed. Exit signs add ISO 7010 or, in the United States, the NFPA 101 legend and letter-height rules. Confirm the specific model number carries the certificate for the country of installation, because UL, EN, and national marks are not interchangeable and an uncertified import can fail inspection even if it is physically capable.

Selection Decision Factors

To turn the preceding chapters into a specific schedule of luminaires, work through the decision sequence below in order. Most emergency-lighting failures at inspection trace not to a single wrong fitting but to a decision made at the wrong level, for example choosing hardware before confirming the code regime and rated duration. These eight steps form a reliable specification template.

1. Code regime and rated duration: First establish whether the building falls under EN 1838 and EN 50172 or under NFPA 101, NEC 700, and the IBC, then fix the rated duration from occupancy: 1 hour for general premises, 3 hours for sleeping or entertainment use under EN 1838, or 90 minutes under NFPA 101.
2. Function and operating mode: Map each location to escape-route, open-area (anti-panic), high-risk task, or exit-sign duty, then select non-maintained or maintained mode to match how the general lighting behaves in that space.
3. Light level and spacing: Use the manufacturer spacing tables or photometric files to place luminaires so the escape-route minimum (1 lux) or open-area minimum (0.5 lux) is met at floor level, with the 40:1 maximum-to-minimum ratio respected and 5 lux delivered at fire-fighting and first-aid points.
4. Power architecture: Choose self-contained for small and medium buildings, central battery with fire-rated cable for hospitals, high-rise, and large estates, or a central static inverter for retrofit of existing fittings. Confirm the transfer time meets the code response limit.
5. Battery chemistry and temperature: Match the chemistry to the measured ambient at the fitting, allowing for ceiling-void heat: LiFePO4 for long life and hot locations, NiCd or NiMH for cost-driven projects, VRLA only in temperature-controlled central cabinets.
6. Ingress protection and hazardous area: Specify IP20 for clean dry interiors, IP65 for car parks, external routes, and washdown, IP66 or IP67 for heavy washdown, and ATEX or IECEx Ex certification to IEC 60079 where flammable gas or dust is present.
7. Test and monitoring regime: Decide between manual, self-test, DALI addressable (IEC 62386-202), or central monitoring, weighing the recurring cost of manual EN 50172 and NFPA 101 monthly and annual tests against the capital cost of automated reporting across the fitting count.
8. Conformity and total cost of ownership: Confirm UL 924 or EN 60598-2-22 certification for the country of installation, then total the lifecycle cost: purchase plus install plus recurring testing labour plus battery replacement over 10 years. Automated self-test and long-life lithium batteries usually win on whole-life cost despite a higher purchase price.

One last dimension is often overlooked: manufacturer serviceability. Long-term compliance depends on the continued availability of matching replacement batteries, spare LED gear trays, and lamp modules, on local technical support for the test and monitoring system, and on documented firmware for addressable fittings. A range that is discontinued or whose battery packs become unobtainable after five years forces premature wholesale replacement. Established suppliers including Eaton (Sure-Lites and CEAG), Hubbell (Dual-Lite), ABB (Emergi-Lite), Signify (Bodine), Zumtobel, and Legrand maintain spare-part and certification support, which is why they remain the default for projects that must stay compliant through audits a decade after handover.