What is the minimum amount of time emergency lighting must be operational during a failure of normal lighting?

The minimum amount of time emergency lighting must be operational during a failure of normal lighting is typically set at 1.5 hours. This requirement is rooted in safety standards that aim to ensure safe evacuation during emergencies, such as power outages or other situations where normal lighting fails. Emergency lighting must be able to support visibility for a sufficient duration, allowing occupants to locate exits and move to safety without the risk of injury.

While other options may seem plausible, they do not meet the established safety standards that dictate a longer operational time for emergency lighting. For example, a duration of 30 minutes would not provide enough time for occupants to evacuate a larger building, especially in emergency situations where panic can slow down response times. Therefore, the 1.5-hour requirement balances the need for effective emergency lighting with the practical consideration of maintaining a safe environment during critical situations.