Emergency Lighting Runtime Screen
Screen emergency and egress lighting battery duration from available energy, emergency load, efficiency, and the required runtime.
Battery and load details
Enter the battery or central-system rated energy before applying the discharge window.
Enter the duration required by the adopted code, listing, design, or AHJ.
Estimated emergency runtime
About this screen
Enter the rated battery energy, usable discharge window, conversion efficiency, emergency lighting load, and required duration. The screen estimates delivered energy, runtime, runtime margin, and the nominal battery energy needed to reach the entered target.
Use it as a design review aid for emergency and egress lighting. It does not replace a listed emergency-lighting system design or an inspection calculation.
Method and assumptions
Usable stored energy equals nominal battery capacity multiplied by the usable discharge percentage. Delivered energy equals usable stored energy multiplied by conversion efficiency. Estimated runtime equals delivered energy divided by emergency load.
The minimum nominal capacity is the energy required for the entered load and duration divided by the entered discharge and efficiency factors. The estimate assumes a steady load and does not model voltage, temperature, aging, discharge-rate, transfer-time, or inverter behavior.
Interpret the result
A passing duration means only that the entered energy and steady-load assumptions reach the entered time. A failed duration identifies an energy shortfall for those inputs; it does not identify the correct battery, fixture count, or emergency power architecture.
FAQs
Should I enter the full lighting-system load?
Enter the load that the emergency source must actually carry during the emergency condition, including connected emergency fixtures and any required control or inverter losses that are not already included in the efficiency value.
What required runtime should I use?
Enter the duration required by the adopted code, equipment listing, design documents, or authority having jurisdiction. A common design target is 90 minutes, but this screen does not choose the requirement for your installation.
Does passing the duration screen approve the emergency-lighting design?
No. Runtime is only one part of the design. Verify photometric coverage, fixture spacing, transfer time, battery discharge behavior, charging, testing, listing, wiring, and emergency-system rules separately.
Sources
- NFPA 101, Life Safety Code — use the adopted edition and local requirements for emergency-lighting duration and system provisions.
- International Building Code, Chapter 10 — public model-code reference for means-of-egress provisions; the adopted code and amendments control.
- Use the emergency-lighting equipment listing, battery documentation, inverter documentation, photometric design, and authority-having-jurisdiction requirements for the actual installation.