Work out emergency lighting duration instantly with clear inputs, formula shown and shareable results.
Emergency lighting duration is usable stored energy divided by connected load. Nameplate ampere hours are derated because deep discharge damages the battery and capacity falls with age, so eighty percent usable is a realistic planning figure. Codes require one hour where evacuation is immediate and three hours where the building may be reoccupied or sleeping risk exists.
Duration
Hours = battery Ah x voltage x usable fraction / load in watts
Preliminary estimate only. Emergency lighting design, duration and testing regime must comply with the applicable standard.
Hours = battery Ah x voltage x usable fraction / load in watts. Emergency lighting duration is usable stored energy divided by connected load.
Battery capacity degrades unpredictably. The annual full duration discharge test is the only reliable evidence that the system still achieves its rated duration.
This calculator takes 4 inputs: Battery capacity, System voltage, Connected emergency load, Usable battery capacity. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.