Emergency Light Symbol
Definition: The Emergency Light symbol represents a self-contained battery-backup egress lighting unit — drawn as a rectangle with two lamp heads on top and a battery cell inside — with Hot, Neutral, and Switched Hot terminals, covered by UL 924 and NEC Article 700 in North America and IEC 60598-2-22 / EN 1838 internationally.
Also known as: emergency lighting unit, twin-head emergency light, battery backup light, egress light, bug-eye light, unit equipment, non-maintained emergency luminaire, frog-eye light.
What the Emergency Light symbol means
The Emergency Light symbol denotes 'unit equipment': a wall- or ceiling-mounted fixture containing a battery, a charger, a transfer relay, and one or more lamp heads (classically two adjustable 'bug-eye' heads). Under normal conditions the unit sits dark while its internal charger, fed from the unswitched Hot and Neutral terminals, float-charges the battery and monitors the supply voltage. When the monitored circuit loses power — a blackout or a tripped breaker on the local lighting circuit — the transfer relay connects the battery to the lamp heads within a fraction of a second, illuminating the exit path.
This behavior is called non-maintained operation: the emergency lamps are OFF when mains power is present and ON only during a supply failure (a maintained fixture, by contrast, is lit at all times). Codes require the unit to sense failure of the branch circuit that feeds the normal lighting in the same area, which is why the connection point matters: the unit must be fed from (or sense) the same circuit, ahead of any local switch, so that someone flipping the room switch off does not falsely trigger emergency mode.
How to identify the Emergency Light symbol
On reflected ceiling plans and wiring diagrams the emergency light appears as a rectangle with two small circles (the lamp heads) on top, often with short radiating lines indicating the beams, and a battery cell symbol (long line/short line pair) drawn inside the rectangle to distinguish it from an ordinary luminaire. A shaded or half-filled fixture symbol with the letters 'EM' or 'E' is the common architectural shorthand.
IEC-style diagrams follow IEC 60617's luminaire symbols with an added battery qualifier and reference IEC 60598-2-22 luminaire classes; European plans often use a square with a diagonal-cross 'safety luminaire' mark from EN 1838 / ISO 30061 practice. North American (ANSI/NECA-style) plans keep the pictorial twin-head rectangle or the 'EM'-tagged luminaire. In both systems, the giveaway is the battery mark plus the connection shown to an unswitched hot.
Function in a circuit
The unit performs three jobs continuously: charging, monitoring, and transfer. The charger converts 120 V or 277 V AC (both are usually accepted via a dual-voltage tap) into a float charge for the internal sealed lead-acid or NiCd/NiMH battery. A voltage-sensing relay watches the Hot terminal; when voltage collapses, the relay drops out and its contacts connect the battery to the LED or halogen lamp heads. Codes require at least 90 minutes of battery runtime at rated output.
The Hot terminal must be an unswitched conductor from the local lighting branch circuit — per NEC 700.12(H), unit equipment must be on the same branch circuit that serves the normal lighting in the area, connected ahead of any local switches (or fed from a dedicated emergency-lighting branch circuit with a lock-on breaker). The Switched Hot terminal, present on combination or dual-function units, lets the heads or an integrated general-purpose lamp also operate as normal lighting under wall-switch control, while the battery/charger stays permanently powered from the unswitched Hot.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60598-2-22 covers luminaires for emergency lighting (self-contained and centrally supplied); EN 1838 / ISO 30061 set the photometric requirements (minimum 1 lux on the escape-route centre line in Europe); EN 50172 covers system application and testing. IEC 60617 provides the base luminaire and battery symbols, with the safety-luminaire variant marked by class labels (non-maintained NM, maintained M). |
|---|---|
| ANSI/IEEE 315 | UL 924 (Emergency Lighting and Power Equipment) is the North American product standard. NEC Article 700 (Emergency Systems) governs the wiring — notably 700.12(H) for unit equipment branch-circuit connection — and NFPA 101 (Life Safety Code) sections 7.8/7.9 require an average of 1 fc (10.8 lux) initial illumination along the egress path and 90 minutes of runtime, plus monthly 30-second and annual 90-minute testing. |
| Key difference | IEC/EN practice distinguishes maintained vs non-maintained luminaire classes explicitly in the symbol and labelling, and specifies illuminance at 1 lux minimum on escape routes; NFPA/UL practice specifies 1 footcandle average initial illumination, a 90-minute duration, and a UL 924 listing, with the fixture drawn pictorially or tagged 'EM'. Wiring rules also differ: NEC ties unit equipment to the local lighting branch circuit, while European rules more commonly use dedicated final circuits or central battery systems. |
Terminals / pins
| Pin | Name |
|---|---|
| hot | Hot |
| neutral | Neutral |
| switched | Switched Hot |
Typical values
Typical North American units accept 120 V and 277 V AC (dual voltage input), draw only 1–5 W while charging, and deliver 90+ minutes of emergency runtime as required by NFPA 101. Modern LED twin heads output roughly 1–4 W per head (replacing 5.4 W halogen wedge lamps), producing several hundred lumens total. Batteries are commonly 3.6–6 V NiCd/NiMH or 6–12 V sealed lead-acid, 1.2–7 Ah. Remote-capable units add DC output terminals (commonly 3.6, 6, or 12 V) rated for a specified remote-head wattage.
Where the Emergency Light symbol is used
- Corridors, stairwells, and exit passageways of commercial buildings where NFPA 101 requires illuminated egress paths
- Assembly occupancies — restaurants, theaters, gyms, churches — above occupant-load thresholds
- Multifamily residential common areas: lobbies, hallways, shared stairways, and parking garages
- Industrial and warehouse spaces, often using higher-output or wet-location-rated twin-head units
- Electrical rooms, mechanical rooms, and generator rooms where codes require egress and task illumination on power loss
- Small offices and retail tenant fit-outs, where combination exit-sign/emergency-light 'combo units' are the standard low-cost solution
Example
In a small-office lighting circuit diagram, the emergency light's Hot pin taps the 20 A lighting branch circuit ahead of the wall switch (unswitched), its Neutral pin lands on the circuit neutral, and the Switched Hot pin connects after the wall switch so the unit's heads can double as normal night lighting. When breaker or utility power fails, the internal relay senses loss of voltage at Hot and transfers both lamp heads to the 6 V 4.5 Ah battery for the code-required 90 minutes.
Key facts
- An emergency light is 'unit equipment' per NEC 700.12(H): a self-contained battery, charger, transfer relay, and lamp heads that switch on automatically when the monitored circuit loses power.
- It must be fed from the same branch circuit as the area's normal lighting, connected ahead of any local switches (or from a dedicated emergency branch circuit with a lock-on breaker) so a wall switch cannot disable it.
- NFPA 101 requires 90 minutes of emergency runtime and an initial average of 1 footcandle (10.8 lux) along the egress path; Europe's EN 1838 requires a minimum of 1 lux on the escape-route centre line.
- Non-maintained operation means the heads are off during normal power and on only during failure; maintained fixtures stay lit at all times.
- The product standard is UL 924 in North America and IEC 60598-2-22 / EN 1838 internationally.
- Required testing is a 30-second functional test monthly and a full 90-minute discharge test annually, typically via the unit's test button or a self-diagnostic feature.
- Modern units use LED heads drawing 1–4 W each and NiCd/NiMH or sealed lead-acid batteries of 3.6–12 V; charging draw is only a few watts.
- Combo units integrate an exit sign and emergency heads in one housing sharing one battery — the most common configuration in small commercial spaces.
Frequently asked questions
What does the emergency light symbol look like on drawings?
The common pictorial symbol is a rectangle with two small circles on top representing the adjustable lamp heads, often with short beam lines, and a battery cell mark inside the rectangle. On architectural reflected ceiling plans it is frequently reduced to a standard luminaire symbol shaded or tagged 'EM' or 'E'. European plans use the EN/IEC safety-luminaire symbol with a maintained (M) or non-maintained (NM) class label.
Why does an emergency light have both a Hot and a Switched Hot terminal?
The unswitched Hot keeps the charger and the power-failure sensing energized 24/7 — this connection must bypass all wall switches so the unit cannot be accidentally disabled. The Switched Hot is used on combination/dual-function units so the lamp heads (or an integrated normal lamp) can also serve as switched general lighting. Basic emergency-only units use just Hot and Neutral.
How long must an emergency light stay on during a power failure?
90 minutes is the requirement in NFPA 101 (Life Safety Code) and the UL 924 listing basis in North America. European standards commonly require 1 hour or 3 hours of rated duration depending on the building category, per EN 1838 and national regulations. The annual test is a full-duration discharge to prove the battery still meets the requirement.
What is the difference between maintained and non-maintained emergency lighting?
A non-maintained fixture is off during normal conditions and lights only when the supply fails — the standard twin-head unit works this way. A maintained fixture is illuminated at all times, running from mains normally and from battery during failure — exit signs are the classic maintained device. IEC/EN labelling marks these classes as NM and M; combination fixtures can do both.
Can I wire an emergency light to any circuit?
No. NEC 700.12(H) requires unit equipment to be connected to the same branch circuit serving the normal lighting in the area, ahead of any local switches — so that a failure of that specific circuit (not just a building-wide outage) triggers the emergency light. The alternative is a dedicated emergency-lighting branch circuit with a locked-on breaker. Plugging one into a random receptacle circuit generally violates this rule.
How often do emergency lights need to be tested?
NFPA 101 requires a 30-second functional test every month and a 90-minute full-duration test every year, with written records kept. Most units have a press-to-test button; self-testing/self-diagnostic models perform these tests automatically and indicate failures with a status LED, which many jurisdictions accept in place of manual testing.
Related symbols
- Battery symbol
- Circuit Breaker symbol
- Fluorescent Fixture symbol
- Light Fixture symbol
- Smoke Detector symbol
- Switch (SPST) symbol
Place the Emergency Light symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.