The proper amount of illumination for an emergency lighting system must be provided for:

• A. 30 minutes
• B. 60 minutes
• C. 120 minutes
• D. 90 minutes

Answer: (D)

Emergency lighting exists to provide visibility for safe egress during a power outage, ensuring occupants can find exits and move to safety even when normal power is out. The standard sets a minimum duration for how long that lighting must be available after failure of the normal power supply. Ninety minutes is the commonly adopted minimum, long enough for evacuation in most occupancies and conditions. Thirty or sixty minutes would often be too short to complete a full evacuation, while a longer duration like one hundred twenty minutes is acceptable in some cases but not the minimum required in this context. So the proper amount of illumination to provide is ninety minutes.