By Kevin Beck, Updated March 24, 2022
When we think of emergency lighting, we often picture flashing police sirens or ambulance beacons. However, the lights that keep a hospital, office building, or theater safe during a power loss are a different category—critical backup illumination that activates automatically when the main supply fails.
Any situation where the normal power supply is interrupted—whether due to a storm, equipment failure, or scheduled outage—constitutes a lighting emergency. In such circumstances, the absence of illumination can impede evacuation, complicate rescue efforts, and compromise safety.
Emergency lighting systems are designed for an instantaneous transition. They rely on a continuously charged battery, maintained by the building’s main supply under normal conditions. When the primary source fails, the battery immediately takes over, providing sufficient illumination for a safe evacuation.
In larger facilities, a backup generator may also be employed. Generators can power the main lighting array to a limited extent while simultaneously recharging onsite batteries, adding an extra layer of protection against prolonged darkness.
Permanent “EXIT” signs, while lit during normal operation, also serve as emergency indicators, ensuring that exit routes remain visible under all conditions.
Typical emergency fixtures comprise a housing, a rechargeable battery, a control circuit board, and a transformer. The battery powers the light source—often LED or fluorescent—while the circuit board and transformer manage battery recharging when the main supply resumes.
Advancements in battery chemistry, such as nickel‑cadmium (Ni‑Cd), have extended the expected lifespan of these systems to two to three years, aligning with routine inspection schedules.
Reliability is paramount. Industry best practice calls for monthly testing of both emergency lights and exit signs. Each unit is powered for a continuous 30‑second interval, sufficient to reveal issues that brief checks might miss.
